<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019fcdef-56b3-7872-8c9a-e5dd11ff4734,g:d20053c7-4dd3-4f66-bcd5-f5c944c1253b-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://lemonade.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="lmnd-20260930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019fcdef-57dd-7d08-b961-4809f007cc39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019fcdef-57dd-729c-8424-a5b8e5b30877" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019fcdef-57dd-7d08-b961-4809f007cc39" xlink:to="loc_us-gaap_StatementTable_019fcdef-57dd-729c-8424-a5b8e5b30877" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fcdef-57dd-7996-a67f-fb85c01b8f54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019fcdef-57dd-729c-8424-a5b8e5b30877" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fcdef-57dd-7996-a67f-fb85c01b8f54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fcdef-57dd-7996-a67f-fb85c01b8f54_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fcdef-57dd-7996-a67f-fb85c01b8f54" xlink:to="loc_us-gaap_EquityComponentDomain_019fcdef-57dd-7996-a67f-fb85c01b8f54_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fcdef-57dd-7df0-92df-253aabd60ac9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fcdef-57dd-7996-a67f-fb85c01b8f54" xlink:to="loc_us-gaap_EquityComponentDomain_019fcdef-57dd-7df0-92df-253aabd60ac9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019fcdef-57dd-7e39-ae69-d5f52cc76aa9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fcdef-57dd-7df0-92df-253aabd60ac9" xlink:to="loc_us-gaap_CommonStockMember_019fcdef-57dd-7e39-ae69-d5f52cc76aa9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019fcdef-57dd-79c2-8d19-becc51238406" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fcdef-57dd-7df0-92df-253aabd60ac9" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019fcdef-57dd-79c2-8d19-becc51238406" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019fcdef-57dd-7516-b918-674db5c96212" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fcdef-57dd-7df0-92df-253aabd60ac9" xlink:to="loc_us-gaap_RetainedEarningsMember_019fcdef-57dd-7516-b918-674db5c96212" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fcdef-57dd-7931-a30c-a3771d66eafd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fcdef-57dd-7df0-92df-253aabd60ac9" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fcdef-57dd-7931-a30c-a3771d66eafd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcdef-57dd-7720-bd06-94ef3dbba7fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fcdef-57dd-7d08-b961-4809f007cc39" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcdef-57dd-7720-bd06-94ef3dbba7fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019fcdef-57dd-75d3-ae04-85e77d4b8a6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcdef-57dd-7720-bd06-94ef3dbba7fb" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019fcdef-57dd-75d3-ae04-85e77d4b8a6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019fcdef-57dd-7272-9395-cfb7caad3eb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcdef-57dd-7720-bd06-94ef3dbba7fb" xlink:to="loc_us-gaap_StockholdersEquity_019fcdef-57dd-7272-9395-cfb7caad3eb7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAndRestrictedStockUnitsExercisesInPeriod_019fcdef-57dd-7618-be0b-22e36c408c84" xlink:href="lmnd-20260930.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAndRestrictedStockUnitsExercisesInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcdef-57dd-7720-bd06-94ef3dbba7fb" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAndRestrictedStockUnitsExercisesInPeriod_019fcdef-57dd-7618-be0b-22e36c408c84" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_StockIssuedDuringPeriodValueStockOptionsAndRestrictedStockExercised_019fcdef-57dd-7f85-bc5c-461c18a55c0e" xlink:href="lmnd-20260930.xsd#lmnd_StockIssuedDuringPeriodValueStockOptionsAndRestrictedStockExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcdef-57dd-7720-bd06-94ef3dbba7fb" xlink:to="loc_lmnd_StockIssuedDuringPeriodValueStockOptionsAndRestrictedStockExercised_019fcdef-57dd-7f85-bc5c-461c18a55c0e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019fcdef-57dd-77bc-9b3b-458acc572855" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcdef-57dd-7720-bd06-94ef3dbba7fb" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019fcdef-57dd-77bc-9b3b-458acc572855" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019fcdef-57dd-7441-9392-d94b7fce520f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcdef-57dd-7720-bd06-94ef3dbba7fb" xlink:to="loc_us-gaap_NetIncomeLoss_019fcdef-57dd-7441-9392-d94b7fce520f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019fcdef-57dd-7425-a067-ed3ba8ef411a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fcdef-57dd-7720-bd06-94ef3dbba7fb" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019fcdef-57dd-7425-a067-ed3ba8ef411a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019fcdef-57dd-70ff-8c11-1e43bb1566c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019fcdef-57dd-77c9-848f-c08141398ec8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/InvestmentsAmortizedCostandFairValuesofInvestmentinFixedMaturitiesDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#InvestmentsAmortizedCostandFairValuesofInvestmentinFixedMaturitiesDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/InvestmentsAmortizedCostandFairValuesofInvestmentinFixedMaturitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcdef-57dd-75a9-8f54-89543074eb82" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcdef-57dd-7e56-bb6d-26dff502e954" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcdef-57dd-75a9-8f54-89543074eb82" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcdef-57dd-7e56-bb6d-26dff502e954" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-74e5-bfc9-f0b333e6e526" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcdef-57dd-7e56-bb6d-26dff502e954" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-74e5-bfc9-f0b333e6e526" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-74e5-bfc9-f0b333e6e526_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-74e5-bfc9-f0b333e6e526" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-74e5-bfc9-f0b333e6e526_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7c3d-8fb8-baadb279fede" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-74e5-bfc9-f0b333e6e526" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7c3d-8fb8-baadb279fede" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019fcdef-57dd-7263-9cc9-eeb58be0cb43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7c3d-8fb8-baadb279fede" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019fcdef-57dd-7263-9cc9-eeb58be0cb43" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019fcdef-57dd-7abf-9395-d5f1f256955c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7c3d-8fb8-baadb279fede" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019fcdef-57dd-7abf-9395-d5f1f256955c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019fcdef-57dd-70b6-87d8-251fb6ff1143" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7c3d-8fb8-baadb279fede" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019fcdef-57dd-70b6-87d8-251fb6ff1143" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fcdef-57dd-74c4-9b3b-aabc4f816d87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7c3d-8fb8-baadb279fede" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fcdef-57dd-74c4-9b3b-aabc4f816d87" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fcdef-57dd-7f7f-a6c3-2fc54981d1ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcdef-57dd-75a9-8f54-89543074eb82" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fcdef-57dd-7f7f-a6c3-2fc54981d1ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019fcdef-57dd-7515-a5a2-e71de4c50e8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcdef-57dd-75a9-8f54-89543074eb82" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019fcdef-57dd-7515-a5a2-e71de4c50e8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fcdef-57dd-706b-aea3-5690026ff85f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcdef-57dd-75a9-8f54-89543074eb82" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fcdef-57dd-706b-aea3-5690026ff85f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019fcdef-57dd-7151-9706-955ccae89feb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcdef-57dd-75a9-8f54-89543074eb82" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019fcdef-57dd-7151-9706-955ccae89feb" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/InvestmentsAdditionalInformationDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#InvestmentsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/InvestmentsAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7d1d-b584-369ce0b5c62c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fcdef-57dd-7d9d-897d-4b0de43e0242" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7d1d-b584-369ce0b5c62c" xlink:to="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fcdef-57dd-7d9d-897d-4b0de43e0242" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7c11-8c7e-57a78f86d1cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fcdef-57dd-7d9d-897d-4b0de43e0242" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7c11-8c7e-57a78f86d1cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7c11-8c7e-57a78f86d1cb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7c11-8c7e-57a78f86d1cb" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7c11-8c7e-57a78f86d1cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-71f4-9c9f-d1e51c123246" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7c11-8c7e-57a78f86d1cb" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-71f4-9c9f-d1e51c123246" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedIncomeSecuritiesMember_019fcdef-57dd-71b1-a0c5-18f0a8e6b438" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedIncomeSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-71f4-9c9f-d1e51c123246" xlink:to="loc_us-gaap_FixedIncomeSecuritiesMember_019fcdef-57dd-71b1-a0c5-18f0a8e6b438" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fcdef-57dd-7557-936f-f94344cafb02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7d1d-b584-369ce0b5c62c" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fcdef-57dd-7557-936f-f94344cafb02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealizedInvestmentGainsLosses_019fcdef-57dd-7a79-b751-bbdf778bf428" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealizedInvestmentGainsLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7d1d-b584-369ce0b5c62c" xlink:to="loc_us-gaap_RealizedInvestmentGainsLosses_019fcdef-57dd-7a79-b751-bbdf778bf428" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019fcdef-57dd-74a4-aab9-58d1d71d6381" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7d1d-b584-369ce0b5c62c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019fcdef-57dd-74a4-aab9-58d1d71d6381" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions_01a1823d-2690-7ef1-a338-1e108dd5d3da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7d1d-b584-369ce0b5c62c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions_01a1823d-2690-7ef1-a338-1e108dd5d3da" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019fcdef-57dd-771e-b66a-0a8fff5d0640" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7d1d-b584-369ce0b5c62c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019fcdef-57dd-771e-b66a-0a8fff5d0640" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedInvestments_019fcdef-57dd-75a1-b03a-0b2729503134" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7d1d-b584-369ce0b5c62c" xlink:to="loc_us-gaap_RestrictedInvestments_019fcdef-57dd-75a1-b03a-0b2729503134" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_019fcdef-57dd-7e14-8406-ad4faabf0a52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7d1d-b584-369ce0b5c62c" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_019fcdef-57dd-7e14-8406-ad4faabf0a52" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/InvestmentsNetInvestmentIncomeDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#InvestmentsNetInvestmentIncomeDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/InvestmentsNetInvestmentIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7f6f-9a75-251cde534452" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fcdef-57dd-7d17-b477-6a29e8db817c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7f6f-9a75-251cde534452" xlink:to="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fcdef-57dd-7d17-b477-6a29e8db817c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019fcdef-57dd-7c8e-b406-094628a09944" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fcdef-57dd-7d17-b477-6a29e8db817c" xlink:to="loc_us-gaap_InvestmentTypeAxis_019fcdef-57dd-7c8e-b406-094628a09944" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019fcdef-57dd-7c8e-b406-094628a09944_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019fcdef-57dd-7c8e-b406-094628a09944" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019fcdef-57dd-7c8e-b406-094628a09944_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019fcdef-57dd-7938-a2b2-8995852a973c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019fcdef-57dd-7c8e-b406-094628a09944" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019fcdef-57dd-7938-a2b2-8995852a973c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsMember_019fcdef-57dd-7f50-8c3c-034b484678d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fcdef-57dd-7938-a2b2-8995852a973c" xlink:to="loc_us-gaap_CashAndCashEquivalentsMember_019fcdef-57dd-7f50-8c3c-034b484678d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019fcdef-57dd-7305-95ae-a11ade7487ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fcdef-57dd-7938-a2b2-8995852a973c" xlink:to="loc_us-gaap_DebtSecuritiesMember_019fcdef-57dd-7305-95ae-a11ade7487ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_019fcdef-57dd-787f-a7cd-ecff768bf213" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fcdef-57dd-7938-a2b2-8995852a973c" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_019fcdef-57dd-787f-a7cd-ecff768bf213" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019fcdef-57dd-79e7-a455-02e9e263a048" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7f6f-9a75-251cde534452" xlink:to="loc_us-gaap_NetInvestmentIncome_019fcdef-57dd-79e7-a455-02e9e263a048" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossInvestmentIncomeOperating_019fcdef-57dd-796c-a42b-fcb2b07a37b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossInvestmentIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7f6f-9a75-251cde534452" xlink:to="loc_us-gaap_GrossInvestmentIncomeOperating_019fcdef-57dd-796c-a42b-fcb2b07a37b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInvestmentExpense_019fcdef-57dd-7cb5-920e-643ce2b2eacd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInvestmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fcdef-57dd-7f6f-9a75-251cde534452" xlink:to="loc_us-gaap_InvestmentIncomeInvestmentExpense_019fcdef-57dd-7cb5-920e-643ce2b2eacd" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/InvestmentsAgingofGrossUnrealizedLossesDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#InvestmentsAgingofGrossUnrealizedLossesDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/InvestmentsAgingofGrossUnrealizedLossesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcdef-57dd-702d-a908-5eccc8bfaf86" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcdef-57dd-708f-9416-1819eaec75cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcdef-57dd-702d-a908-5eccc8bfaf86" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcdef-57dd-708f-9416-1819eaec75cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7f66-91fe-aac3ba1abad1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fcdef-57dd-708f-9416-1819eaec75cd" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7f66-91fe-aac3ba1abad1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7f66-91fe-aac3ba1abad1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7f66-91fe-aac3ba1abad1" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7f66-91fe-aac3ba1abad1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-73df-8c23-eb7d49fc6c8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7f66-91fe-aac3ba1abad1" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-73df-8c23-eb7d49fc6c8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019fcdef-57dd-7fb2-b4a4-322262fa86c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-73df-8c23-eb7d49fc6c8e" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019fcdef-57dd-7fb2-b4a4-322262fa86c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019fcdef-57dd-7ba2-8975-82363b330419" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-73df-8c23-eb7d49fc6c8e" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019fcdef-57dd-7ba2-8975-82363b330419" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019fcdef-57dd-7e21-b43f-0596de223ef2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-73df-8c23-eb7d49fc6c8e" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019fcdef-57dd-7e21-b43f-0596de223ef2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fcdef-57dd-7644-870c-42ab6f950416" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-73df-8c23-eb7d49fc6c8e" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fcdef-57dd-7644-870c-42ab6f950416" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAbstract_019fcdef-57dd-7d09-8705-025caa906fd2" xlink:href="lmnd-20260930.xsd#lmnd_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcdef-57dd-702d-a908-5eccc8bfaf86" xlink:to="loc_lmnd_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAbstract_019fcdef-57dd-7d09-8705-025caa906fd2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019fcdef-57dd-74e1-b14a-1cd1131a0afb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAbstract_019fcdef-57dd-7d09-8705-025caa906fd2" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019fcdef-57dd-74e1-b14a-1cd1131a0afb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019fcdef-57dd-7af2-a7d3-8214b08e47c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAbstract_019fcdef-57dd-7d09-8705-025caa906fd2" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019fcdef-57dd-7af2-a7d3-8214b08e47c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019fcdef-57dd-7218-85e3-307739cfa69f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAbstract_019fcdef-57dd-7d09-8705-025caa906fd2" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019fcdef-57dd-7218-85e3-307739cfa69f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fcdef-57dd-7ca8-87f1-863f81cfa1d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fcdef-57dd-702d-a908-5eccc8bfaf86" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fcdef-57dd-7ca8-87f1-863f81cfa1d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019fcdef-57dd-794a-a860-1826ebb2fd0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fcdef-57dd-7ca8-87f1-863f81cfa1d4" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019fcdef-57dd-794a-a860-1826ebb2fd0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019fcdef-57dd-7baa-9285-101c43f10b80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fcdef-57dd-7ca8-87f1-863f81cfa1d4" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019fcdef-57dd-7baa-9285-101c43f10b80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_019fcdef-57dd-7b63-ac66-5adfbcde9061" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fcdef-57dd-7ca8-87f1-863f81cfa1d4" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_019fcdef-57dd-7b63-ac66-5adfbcde9061" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_01a1a1c9-bbd2-7928-abd6-49b8dc76ae51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/FairValueMeasurementsFairValueHierarchyforFinancialAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#FairValueMeasurementsFairValueHierarchyforFinancialAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/FairValueMeasurementsFairValueHierarchyforFinancialAssetsandLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fcdef-57dd-70b3-9399-76dc450d3e27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fcdef-57dd-782e-8bf6-1bf66872c17e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fcdef-57dd-70b3-9399-76dc450d3e27" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fcdef-57dd-782e-8bf6-1bf66872c17e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fcdef-57dd-7633-8cf7-45700b5876d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fcdef-57dd-782e-8bf6-1bf66872c17e" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fcdef-57dd-7633-8cf7-45700b5876d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcdef-57dd-7633-8cf7-45700b5876d0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fcdef-57dd-7633-8cf7-45700b5876d0" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcdef-57dd-7633-8cf7-45700b5876d0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcdef-57dd-7c1c-a84b-9bb925991d98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fcdef-57dd-7633-8cf7-45700b5876d0" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcdef-57dd-7c1c-a84b-9bb925991d98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019fcdef-57dd-715c-8e6a-6f37563bf455" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcdef-57dd-7c1c-a84b-9bb925991d98" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019fcdef-57dd-715c-8e6a-6f37563bf455" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019fcdef-57dd-7ec7-af36-4e9d03cf7200" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcdef-57dd-7c1c-a84b-9bb925991d98" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019fcdef-57dd-7ec7-af36-4e9d03cf7200" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019fcdef-57dd-7cc9-a1c4-8a7f7a651adf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fcdef-57dd-7c1c-a84b-9bb925991d98" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019fcdef-57dd-7cc9-a1c4-8a7f7a651adf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7c8d-bbb2-86a67cedab9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fcdef-57dd-782e-8bf6-1bf66872c17e" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7c8d-bbb2-86a67cedab9a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7c8d-bbb2-86a67cedab9a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7c8d-bbb2-86a67cedab9a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-7c8d-bbb2-86a67cedab9a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-77da-bcf8-b8966a5cb5b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fcdef-57dd-7c8d-bbb2-86a67cedab9a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-77da-bcf8-b8966a5cb5b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019fcdef-57dd-7f5e-8968-74024cded409" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-77da-bcf8-b8966a5cb5b5" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019fcdef-57dd-7f5e-8968-74024cded409" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019fcdef-57dd-796f-a092-e27b9f5fdb52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-77da-bcf8-b8966a5cb5b5" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019fcdef-57dd-796f-a092-e27b9f5fdb52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AssetBackedSecuritiesAndCollateralizedLoanObligationsMember_019fcdef-57dd-7b42-8777-35b830a0e6d8" xlink:href="lmnd-20260930.xsd#lmnd_AssetBackedSecuritiesAndCollateralizedLoanObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-77da-bcf8-b8966a5cb5b5" xlink:to="loc_lmnd_AssetBackedSecuritiesAndCollateralizedLoanObligationsMember_019fcdef-57dd-7b42-8777-35b830a0e6d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fcdef-57dd-7327-8f3d-edcb30cb975c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-77da-bcf8-b8966a5cb5b5" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fcdef-57dd-7327-8f3d-edcb30cb975c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019fcdef-57dd-7d82-bacf-5984682ff860" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fcdef-57dd-77da-bcf8-b8966a5cb5b5" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019fcdef-57dd-7d82-bacf-5984682ff860" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019fcdef-57dd-7dde-b2fb-1b94d5ed8e3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fcdef-57dd-70b3-9399-76dc450d3e27" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019fcdef-57dd-7dde-b2fb-1b94d5ed8e3b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestments_019fcdef-57dd-7e75-9a67-07f4b555776b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fcdef-57dd-70b3-9399-76dc450d3e27" xlink:to="loc_us-gaap_ShortTermInvestments_019fcdef-57dd-7e75-9a67-07f4b555776b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019fcdef-57dd-78b3-93c7-2e3e5bf6d8dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fcdef-57dd-70b3-9399-76dc450d3e27" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019fcdef-57dd-78b3-93c7-2e3e5bf6d8dc" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/UnpaidLossandLossAdjustmentExpenseNarrativeDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#UnpaidLossandLossAdjustmentExpenseNarrativeDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/UnpaidLossandLossAdjustmentExpenseNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOfReinsuranceLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectsOfReinsuranceTable_019fcdef-57dd-765a-b4e9-47bea505f151" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOfReinsuranceTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_EffectsOfReinsuranceTable_019fcdef-57dd-765a-b4e9-47bea505f151" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7492-99f9-c80d0ff97ff9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualOrInfrequentItemAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019fcdef-57dd-765a-b4e9-47bea505f151" xlink:to="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7492-99f9-c80d0ff97ff9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7492-99f9-c80d0ff97ff9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualOrInfrequentItemDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7492-99f9-c80d0ff97ff9" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7492-99f9-c80d0ff97ff9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7268-ad8b-5816976bb2fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualOrInfrequentItemDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7492-99f9-c80d0ff97ff9" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7268-ad8b-5816976bb2fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CaliforniaWildfiresMember_019fcdef-57dd-7848-b95f-39729d0f7718" xlink:href="lmnd-20260930.xsd#lmnd_CaliforniaWildfiresMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7268-ad8b-5816976bb2fb" xlink:to="loc_lmnd_CaliforniaWildfiresMember_019fcdef-57dd-7848-b95f-39729d0f7718" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fcdef-57dd-7bb8-9f95-d05a9aa67a08" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019fcdef-57dd-765a-b4e9-47bea505f151" xlink:to="loc_srt_RangeAxis_019fcdef-57dd-7bb8-9f95-d05a9aa67a08" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fcdef-57dd-7bb8-9f95-d05a9aa67a08_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fcdef-57dd-7bb8-9f95-d05a9aa67a08" xlink:to="loc_srt_RangeMember_019fcdef-57dd-7bb8-9f95-d05a9aa67a08_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fcdef-57dd-7e17-a78c-b574d12d4cdd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fcdef-57dd-7bb8-9f95-d05a9aa67a08" xlink:to="loc_srt_RangeMember_019fcdef-57dd-7e17-a78c-b574d12d4cdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fcdef-57dd-795c-adfd-f47c6dd333bf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fcdef-57dd-7e17-a78c-b574d12d4cdd" xlink:to="loc_srt_MaximumMember_019fcdef-57dd-795c-adfd-f47c6dd333bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fcdef-57dd-7a23-b132-d0b39fe58261" xlink:href="lmnd-20260930.xsd#lmnd_ReinsuranceArrangementByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019fcdef-57dd-765a-b4e9-47bea505f151" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fcdef-57dd-7a23-b132-d0b39fe58261" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7a23-b132-d0b39fe58261_default" xlink:href="lmnd-20260930.xsd#lmnd_ReinsuranceArrangementByTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fcdef-57dd-7a23-b132-d0b39fe58261" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7a23-b132-d0b39fe58261_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7455-b60a-9dda65890e36" xlink:href="lmnd-20260930.xsd#lmnd_ReinsuranceArrangementByTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fcdef-57dd-7a23-b132-d0b39fe58261" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7455-b60a-9dda65890e36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_MICQuotaShareReinsuranceContractMember_019fcdef-57dd-72d5-a13c-55951effe943" xlink:href="lmnd-20260930.xsd#lmnd_MICQuotaShareReinsuranceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7455-b60a-9dda65890e36" xlink:to="loc_lmnd_MICQuotaShareReinsuranceContractMember_019fcdef-57dd-72d5-a13c-55951effe943" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LICQuotaShareReinsuranceContractMember_019fcdef-57dd-7fe3-8d20-a5f1605a98ce" xlink:href="lmnd-20260930.xsd#lmnd_LICQuotaShareReinsuranceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7455-b60a-9dda65890e36" xlink:to="loc_lmnd_LICQuotaShareReinsuranceContractMember_019fcdef-57dd-7fe3-8d20-a5f1605a98ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceContractAxis_019fcdef-57dd-766c-a7a1-6baf61eff07c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReinsuranceContractAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019fcdef-57dd-765a-b4e9-47bea505f151" xlink:to="loc_us-gaap_ReinsuranceContractAxis_019fcdef-57dd-766c-a7a1-6baf61eff07c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019fcdef-57dd-75f6-a442-30ff02ef958a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019fcdef-57dd-75f6-a442-30ff02ef958a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_019fcdef-57dd-76cb-9f8c-2747121b3225" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_019fcdef-57dd-76cb-9f8c-2747121b3225" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease_019fcdef-57dd-7857-9c58-aa56339be05f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease_019fcdef-57dd-7857-9c58-aa56339be05f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage_019fcdef-57dd-7aae-95e9-cfeff2e936f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage_019fcdef-57dd-7aae-95e9-cfeff2e936f8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerEvent_019fcdef-57dd-71a3-8f19-98305a247ec2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerEvent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerEvent_019fcdef-57dd-71a3-8f19-98305a247ec2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsurancePerRiskLimitAmount_019fcdef-57dd-7f10-a104-f8978f93314a" xlink:href="lmnd-20260930.xsd#lmnd_ReinsurancePerRiskLimitAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_lmnd_ReinsurancePerRiskLimitAmount_019fcdef-57dd-7f10-a104-f8978f93314a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionAmountRetainedPerEvent_019fcdef-57dd-71f3-ad21-7e2b22ee5b9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReinsuranceRetentionAmountRetainedPerEvent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_ReinsuranceRetentionAmountRetainedPerEvent_019fcdef-57dd-71f3-ad21-7e2b22ee5b9d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsurancePaymentsToSettleContract_01a1429c-ddbb-79b5-8520-3eef6ba11c78" xlink:href="lmnd-20260930.xsd#lmnd_ReinsurancePaymentsToSettleContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_lmnd_ReinsurancePaymentsToSettleContract_01a1429c-ddbb-79b5-8520-3eef6ba11c78" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_GainLossOnCommutationOfReinsuranceContracts_01a19b67-f798-7429-a97e-a7cc2807180a" xlink:href="lmnd-20260930.xsd#lmnd_GainLossOnCommutationOfReinsuranceContracts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_lmnd_GainLossOnCommutationOfReinsuranceContracts_01a19b67-f798-7429-a97e-a7cc2807180a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerPolicy_019fcdef-57dd-737a-b246-f1dc290b6e42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerPolicy"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerPolicy_019fcdef-57dd-737a-b246-f1dc290b6e42" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionPolicyExcessRetentionPercentage_019fcdef-57dd-724c-9117-03b982e6bf8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReinsuranceRetentionPolicyExcessRetentionPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_ReinsuranceRetentionPolicyExcessRetentionPercentage_019fcdef-57dd-724c-9117-03b982e6bf8f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_PercentageOfDeferredReinsuranceCedingCommissions_019fcdef-57dd-76c6-92d1-7d0f24081633" xlink:href="lmnd-20260930.xsd#lmnd_PercentageOfDeferredReinsuranceCedingCommissions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_lmnd_PercentageOfDeferredReinsuranceCedingCommissions_019fcdef-57dd-76c6-92d1-7d0f24081633" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/UnpaidLossandLossAdjustmentExpenseNarrativeDetails_1" xlink:type="simple" xlink:href="lmnd-20260930.xsd#UnpaidLossandLossAdjustmentExpenseNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/UnpaidLossandLossAdjustmentExpenseNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOfReinsuranceLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectsOfReinsuranceTable_019fcdef-57dd-765a-b4e9-47bea505f151" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectsOfReinsuranceTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_EffectsOfReinsuranceTable_019fcdef-57dd-765a-b4e9-47bea505f151" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7492-99f9-c80d0ff97ff9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualOrInfrequentItemAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019fcdef-57dd-765a-b4e9-47bea505f151" xlink:to="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7492-99f9-c80d0ff97ff9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7492-99f9-c80d0ff97ff9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualOrInfrequentItemDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7492-99f9-c80d0ff97ff9" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7492-99f9-c80d0ff97ff9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7268-ad8b-5816976bb2fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualOrInfrequentItemDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7492-99f9-c80d0ff97ff9" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7268-ad8b-5816976bb2fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CaliforniaWildfiresMember_019fcdef-57dd-7848-b95f-39729d0f7718" xlink:href="lmnd-20260930.xsd#lmnd_CaliforniaWildfiresMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7268-ad8b-5816976bb2fb" xlink:to="loc_lmnd_CaliforniaWildfiresMember_019fcdef-57dd-7848-b95f-39729d0f7718" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fcdef-57dd-7bb8-9f95-d05a9aa67a08" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019fcdef-57dd-765a-b4e9-47bea505f151" xlink:to="loc_srt_RangeAxis_019fcdef-57dd-7bb8-9f95-d05a9aa67a08" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fcdef-57dd-7bb8-9f95-d05a9aa67a08_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fcdef-57dd-7bb8-9f95-d05a9aa67a08" xlink:to="loc_srt_RangeMember_019fcdef-57dd-7bb8-9f95-d05a9aa67a08_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fcdef-57dd-7e17-a78c-b574d12d4cdd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fcdef-57dd-7bb8-9f95-d05a9aa67a08" xlink:to="loc_srt_RangeMember_019fcdef-57dd-7e17-a78c-b574d12d4cdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fcdef-57dd-795c-adfd-f47c6dd333bf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fcdef-57dd-7e17-a78c-b574d12d4cdd" xlink:to="loc_srt_MaximumMember_019fcdef-57dd-795c-adfd-f47c6dd333bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fcdef-57dd-7a23-b132-d0b39fe58261" xlink:href="lmnd-20260930.xsd#lmnd_ReinsuranceArrangementByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019fcdef-57dd-765a-b4e9-47bea505f151" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fcdef-57dd-7a23-b132-d0b39fe58261" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7a23-b132-d0b39fe58261_default" xlink:href="lmnd-20260930.xsd#lmnd_ReinsuranceArrangementByTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fcdef-57dd-7a23-b132-d0b39fe58261" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7a23-b132-d0b39fe58261_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7455-b60a-9dda65890e36" xlink:href="lmnd-20260930.xsd#lmnd_ReinsuranceArrangementByTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fcdef-57dd-7a23-b132-d0b39fe58261" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7455-b60a-9dda65890e36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_MICQuotaShareReinsuranceContractMember_019fcdef-57dd-72d5-a13c-55951effe943" xlink:href="lmnd-20260930.xsd#lmnd_MICQuotaShareReinsuranceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7455-b60a-9dda65890e36" xlink:to="loc_lmnd_MICQuotaShareReinsuranceContractMember_019fcdef-57dd-72d5-a13c-55951effe943" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LICQuotaShareReinsuranceContractMember_019fcdef-57dd-7fe3-8d20-a5f1605a98ce" xlink:href="lmnd-20260930.xsd#lmnd_LICQuotaShareReinsuranceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fcdef-57dd-7455-b60a-9dda65890e36" xlink:to="loc_lmnd_LICQuotaShareReinsuranceContractMember_019fcdef-57dd-7fe3-8d20-a5f1605a98ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019fcdef-57dd-75f6-a442-30ff02ef958a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019fcdef-57dd-75f6-a442-30ff02ef958a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_019fcdef-57dd-76cb-9f8c-2747121b3225" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_019fcdef-57dd-76cb-9f8c-2747121b3225" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease_019fcdef-57dd-7857-9c58-aa56339be05f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease_019fcdef-57dd-7857-9c58-aa56339be05f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage_019fcdef-57dd-7aae-95e9-cfeff2e936f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage_019fcdef-57dd-7aae-95e9-cfeff2e936f8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerEvent_019fcdef-57dd-71a3-8f19-98305a247ec2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerEvent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerEvent_019fcdef-57dd-71a3-8f19-98305a247ec2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsurancePerRiskLimitAmount_019fcdef-57dd-7f10-a104-f8978f93314a" xlink:href="lmnd-20260930.xsd#lmnd_ReinsurancePerRiskLimitAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_lmnd_ReinsurancePerRiskLimitAmount_019fcdef-57dd-7f10-a104-f8978f93314a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionAmountRetainedPerEvent_019fcdef-57dd-71f3-ad21-7e2b22ee5b9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReinsuranceRetentionAmountRetainedPerEvent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_ReinsuranceRetentionAmountRetainedPerEvent_019fcdef-57dd-71f3-ad21-7e2b22ee5b9d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsurancePaymentsToSettleContract_01a1429c-ddbb-79b5-8520-3eef6ba11c78" xlink:href="lmnd-20260930.xsd#lmnd_ReinsurancePaymentsToSettleContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_lmnd_ReinsurancePaymentsToSettleContract_01a1429c-ddbb-79b5-8520-3eef6ba11c78" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_GainLossOnCommutationOfReinsuranceContracts_01a19b67-f798-7429-a97e-a7cc2807180a" xlink:href="lmnd-20260930.xsd#lmnd_GainLossOnCommutationOfReinsuranceContracts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_lmnd_GainLossOnCommutationOfReinsuranceContracts_01a19b67-f798-7429-a97e-a7cc2807180a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerPolicy_019fcdef-57dd-737a-b246-f1dc290b6e42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerPolicy"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerPolicy_019fcdef-57dd-737a-b246-f1dc290b6e42" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionPolicyExcessRetentionPercentage_019fcdef-57dd-724c-9117-03b982e6bf8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReinsuranceRetentionPolicyExcessRetentionPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_us-gaap_ReinsuranceRetentionPolicyExcessRetentionPercentage_019fcdef-57dd-724c-9117-03b982e6bf8f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_PercentageOfDeferredReinsuranceCedingCommissions_019fcdef-57dd-76c6-92d1-7d0f24081633" xlink:href="lmnd-20260930.xsd#lmnd_PercentageOfDeferredReinsuranceCedingCommissions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019fcdef-57dd-7b24-a57a-5901760d5226" xlink:to="loc_lmnd_PercentageOfDeferredReinsuranceCedingCommissions_019fcdef-57dd-76c6-92d1-7d0f24081633" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/BorrowingsunderFinancingAgreementDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#BorrowingsunderFinancingAgreementDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/BorrowingsunderFinancingAgreementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019fcdef-57dd-78bd-80d8-1fc6599b829f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:to="loc_us-gaap_DebtInstrumentTable_019fcdef-57dd-78bd-80d8-1fc6599b829f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fcdef-57dd-7dc0-96f0-e343ae8b82fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fcdef-57dd-78bd-80d8-1fc6599b829f" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fcdef-57dd-7dc0-96f0-e343ae8b82fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fcdef-57dd-7dc0-96f0-e343ae8b82fd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fcdef-57dd-7dc0-96f0-e343ae8b82fd" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fcdef-57dd-7dc0-96f0-e343ae8b82fd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fcdef-57dd-78bc-ba15-b0ab7575b438" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fcdef-57dd-7dc0-96f0-e343ae8b82fd" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fcdef-57dd-78bc-ba15-b0ab7575b438" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CustomerInvestmentAgreementMember_019fcdef-57dd-78b4-b9bb-af920aa81312" xlink:href="lmnd-20260930.xsd#lmnd_CustomerInvestmentAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fcdef-57dd-78bc-ba15-b0ab7575b438" xlink:to="loc_lmnd_CustomerInvestmentAgreementMember_019fcdef-57dd-78b4-b9bb-af920aa81312" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AmendedAndRestatedCustomerInvestmentAgreementMember_019fcdef-57dd-7d09-b0d4-5bcaca781be3" xlink:href="lmnd-20260930.xsd#lmnd_AmendedAndRestatedCustomerInvestmentAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fcdef-57dd-78bc-ba15-b0ab7575b438" xlink:to="loc_lmnd_AmendedAndRestatedCustomerInvestmentAgreementMember_019fcdef-57dd-7d09-b0d4-5bcaca781be3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_NewBusinessFinancingAgreementMember_019fcdef-57dd-73ca-963f-df346d317b91" xlink:href="lmnd-20260930.xsd#lmnd_NewBusinessFinancingAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fcdef-57dd-78bc-ba15-b0ab7575b438" xlink:to="loc_lmnd_NewBusinessFinancingAgreementMember_019fcdef-57dd-73ca-963f-df346d317b91" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fcdef-57dd-7254-8691-b50a64c1dbab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fcdef-57dd-78bd-80d8-1fc6599b829f" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fcdef-57dd-7254-8691-b50a64c1dbab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fcdef-57dd-7254-8691-b50a64c1dbab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fcdef-57dd-7254-8691-b50a64c1dbab" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fcdef-57dd-7254-8691-b50a64c1dbab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fcdef-57dd-7cca-898c-d4c2d6de1500" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fcdef-57dd-7254-8691-b50a64c1dbab" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fcdef-57dd-7cca-898c-d4c2d6de1500" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019fcdef-57dd-7e5a-a4f4-2dd9ea0d72ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fcdef-57dd-7cca-898c-d4c2d6de1500" xlink:to="loc_us-gaap_LineOfCreditMember_019fcdef-57dd-7e5a-a4f4-2dd9ea0d72ba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fcdef-57dd-7742-a910-9609e4875d0b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fcdef-57dd-78bd-80d8-1fc6599b829f" xlink:to="loc_srt_RangeAxis_019fcdef-57dd-7742-a910-9609e4875d0b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fcdef-57dd-7742-a910-9609e4875d0b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fcdef-57dd-7742-a910-9609e4875d0b" xlink:to="loc_srt_RangeMember_019fcdef-57dd-7742-a910-9609e4875d0b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fcdef-57dd-7a6e-856e-a48dc064e1f2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fcdef-57dd-7742-a910-9609e4875d0b" xlink:to="loc_srt_RangeMember_019fcdef-57dd-7a6e-856e-a48dc064e1f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fcdef-57dd-7c4c-9e36-86d0a7db9e6d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fcdef-57dd-7a6e-856e-a48dc064e1f2" xlink:to="loc_srt_MinimumMember_019fcdef-57dd-7c4c-9e36-86d0a7db9e6d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fcdef-57dd-7d7a-b82a-4f398a1c6ae5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fcdef-57dd-7a6e-856e-a48dc064e1f2" xlink:to="loc_srt_MaximumMember_019fcdef-57dd-7d7a-b82a-4f398a1c6ae5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7ec3-b187-a1b64231ef6e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fcdef-57dd-78bd-80d8-1fc6599b829f" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7ec3-b187-a1b64231ef6e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7ec3-b187-a1b64231ef6e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7ec3-b187-a1b64231ef6e" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7ec3-b187-a1b64231ef6e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-714c-bc09-5ad4c8151e75" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7ec3-b187-a1b64231ef6e" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-714c-bc09-5ad4c8151e75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_GCCustomerValueArrangerLLCMember_019fcdef-57dd-7147-9eca-fb94ad60ee29" xlink:href="lmnd-20260930.xsd#lmnd_GCCustomerValueArrangerLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-714c-bc09-5ad4c8151e75" xlink:to="loc_lmnd_GCCustomerValueArrangerLLCMember_019fcdef-57dd-7147-9eca-fb94ad60ee29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtInstrumentFundingPeriodAxis_019fcdef-57dd-740d-93ce-9a55328755e0" xlink:href="lmnd-20260930.xsd#lmnd_DebtInstrumentFundingPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fcdef-57dd-78bd-80d8-1fc6599b829f" xlink:to="loc_lmnd_DebtInstrumentFundingPeriodAxis_019fcdef-57dd-740d-93ce-9a55328755e0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtInstrumentFundingPeriodDomain_019fcdef-57dd-740d-93ce-9a55328755e0_default" xlink:href="lmnd-20260930.xsd#lmnd_DebtInstrumentFundingPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_lmnd_DebtInstrumentFundingPeriodAxis_019fcdef-57dd-740d-93ce-9a55328755e0" xlink:to="loc_lmnd_DebtInstrumentFundingPeriodDomain_019fcdef-57dd-740d-93ce-9a55328755e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtInstrumentFundingPeriodDomain_019fcdef-57dd-7887-9351-6735490014c7" xlink:href="lmnd-20260930.xsd#lmnd_DebtInstrumentFundingPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_lmnd_DebtInstrumentFundingPeriodAxis_019fcdef-57dd-740d-93ce-9a55328755e0" xlink:to="loc_lmnd_DebtInstrumentFundingPeriodDomain_019fcdef-57dd-7887-9351-6735490014c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtInstrumentFundingPeriodOneMember_019fcdef-57dd-7cb3-8b93-fc3d01eb0f13" xlink:href="lmnd-20260930.xsd#lmnd_DebtInstrumentFundingPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_DebtInstrumentFundingPeriodDomain_019fcdef-57dd-7887-9351-6735490014c7" xlink:to="loc_lmnd_DebtInstrumentFundingPeriodOneMember_019fcdef-57dd-7cb3-8b93-fc3d01eb0f13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtInstrumentFundingPeriodTwoMember_019fcdef-57dd-7002-9cd1-65a639baf59b" xlink:href="lmnd-20260930.xsd#lmnd_DebtInstrumentFundingPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_DebtInstrumentFundingPeriodDomain_019fcdef-57dd-7887-9351-6735490014c7" xlink:to="loc_lmnd_DebtInstrumentFundingPeriodTwoMember_019fcdef-57dd-7002-9cd1-65a639baf59b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019fcdef-57dd-7e53-8646-b8c568370f77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fcdef-57dd-78bd-80d8-1fc6599b829f" xlink:to="loc_us-gaap_VariableRateAxis_019fcdef-57dd-7e53-8646-b8c568370f77" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019fcdef-57dd-7e53-8646-b8c568370f77_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019fcdef-57dd-7e53-8646-b8c568370f77" xlink:to="loc_us-gaap_VariableRateDomain_019fcdef-57dd-7e53-8646-b8c568370f77_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019fcdef-57dd-7c40-9381-b06657bc44d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019fcdef-57dd-7e53-8646-b8c568370f77" xlink:to="loc_us-gaap_VariableRateDomain_019fcdef-57dd-7c40-9381-b06657bc44d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReferencePremiumMember_019fcdef-57dd-7c62-9f75-3cd68a99ae56" xlink:href="lmnd-20260930.xsd#lmnd_ReferencePremiumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019fcdef-57dd-7c40-9381-b06657bc44d4" xlink:to="loc_lmnd_ReferencePremiumMember_019fcdef-57dd-7c62-9f75-3cd68a99ae56" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ThreeYearU.S.TreasuryBillRateMember_019fcdef-57dd-7aa9-8b94-bf073b017d3e" xlink:href="lmnd-20260930.xsd#lmnd_ThreeYearU.S.TreasuryBillRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019fcdef-57dd-7c40-9381-b06657bc44d4" xlink:to="loc_lmnd_ThreeYearU.S.TreasuryBillRateMember_019fcdef-57dd-7aa9-8b94-bf073b017d3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019fcdef-57dd-78be-9b7c-9481eaf3c313" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019fcdef-57dd-78be-9b7c-9481eaf3c313" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_019fcdef-57dd-779d-b193-ccbdfd611119" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:to="loc_us-gaap_DebtInstrumentTerm_019fcdef-57dd-779d-b193-ccbdfd611119" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LineOfCreditFacilityAdditionalBorrowingCapacity_019fcdef-57dd-79c5-b710-4e87aa2ddcd1" xlink:href="lmnd-20260930.xsd#lmnd_LineOfCreditFacilityAdditionalBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:to="loc_lmnd_LineOfCreditFacilityAdditionalBorrowingCapacity_019fcdef-57dd-79c5-b710-4e87aa2ddcd1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_InvestmentInEquitySecuritiesFVNIPercentageOfGrowthSpend_019fcdef-57dd-73a7-8327-7ec15baa9ba2" xlink:href="lmnd-20260930.xsd#lmnd_InvestmentInEquitySecuritiesFVNIPercentageOfGrowthSpend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:to="loc_lmnd_InvestmentInEquitySecuritiesFVNIPercentageOfGrowthSpend_019fcdef-57dd-73a7-8327-7ec15baa9ba2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_InvestmentInEquitySecuritiesFVNIInternalRateOfReturnPercent_019fcdef-57dd-7e57-aa71-ffe73c222168" xlink:href="lmnd-20260930.xsd#lmnd_InvestmentInEquitySecuritiesFVNIInternalRateOfReturnPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:to="loc_lmnd_InvestmentInEquitySecuritiesFVNIInternalRateOfReturnPercent_019fcdef-57dd-7e57-aa71-ffe73c222168" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019fcdef-57dd-745f-96b2-7f487b21d0f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:to="loc_us-gaap_LongTermDebt_019fcdef-57dd-745f-96b2-7f487b21d0f9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_019fcdef-57dd-7957-9a1a-cf5aacc52047" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:to="loc_us-gaap_InterestExpenseDebt_019fcdef-57dd-7957-9a1a-cf5aacc52047" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LineOfCreditFacilityFundingPercentageOfMonthlyGrowthSpend_019fcdef-57dd-74cc-a9d5-3895e079d48f" xlink:href="lmnd-20260930.xsd#lmnd_LineOfCreditFacilityFundingPercentageOfMonthlyGrowthSpend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:to="loc_lmnd_LineOfCreditFacilityFundingPercentageOfMonthlyGrowthSpend_019fcdef-57dd-74cc-a9d5-3895e079d48f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LineOfCreditFacilityMaximumBorrowingCapacityPerReferenceCohort_019fcdef-57dd-7f13-8aed-19af6787bee2" xlink:href="lmnd-20260930.xsd#lmnd_LineOfCreditFacilityMaximumBorrowingCapacityPerReferenceCohort"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:to="loc_lmnd_LineOfCreditFacilityMaximumBorrowingCapacityPerReferenceCohort_019fcdef-57dd-7f13-8aed-19af6787bee2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019fcdef-57dd-7f74-bcbe-bf2aae1acb52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fcdef-57dd-7b98-b966-47decba43c6e" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019fcdef-57dd-7f74-bcbe-bf2aae1acb52" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/StockholdersEquityDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#StockholdersEquityDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/StockholdersEquityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019fcdef-57dd-77d6-99df-19a3a14c46f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019fcdef-57dd-77d6-99df-19a3a14c46f6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019fcdef-57dd-7290-91b4-31e7a9e1bf56" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019fcdef-57dd-77d6-99df-19a3a14c46f6" xlink:to="loc_srt_CounterpartyNameAxis_019fcdef-57dd-7290-91b4-31e7a9e1bf56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fcdef-57dd-7290-91b4-31e7a9e1bf56_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019fcdef-57dd-7290-91b4-31e7a9e1bf56" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fcdef-57dd-7290-91b4-31e7a9e1bf56_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fcdef-57dd-715d-b94c-51103a027319" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019fcdef-57dd-7290-91b4-31e7a9e1bf56" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fcdef-57dd-715d-b94c-51103a027319" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeFoundationMember_019fcdef-57dd-7eb1-b231-3f67d52a7624" xlink:href="lmnd-20260930.xsd#lmnd_LemonadeFoundationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fcdef-57dd-715d-b94c-51103a027319" xlink:to="loc_lmnd_LemonadeFoundationMember_019fcdef-57dd-7eb1-b231-3f67d52a7624" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fcdef-57dd-78ad-9c1a-2704f23d8999" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019fcdef-57dd-77d6-99df-19a3a14c46f6" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fcdef-57dd-78ad-9c1a-2704f23d8999" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fcdef-57dd-78ad-9c1a-2704f23d8999_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fcdef-57dd-78ad-9c1a-2704f23d8999" xlink:to="loc_us-gaap_RelatedPartyDomain_019fcdef-57dd-78ad-9c1a-2704f23d8999_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fcdef-57dd-78c8-8a75-cdd33af56654" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fcdef-57dd-78ad-9c1a-2704f23d8999" xlink:to="loc_us-gaap_RelatedPartyDomain_019fcdef-57dd-78c8-8a75-cdd33af56654" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_019fcdef-57dd-715d-965f-fc0c8d44266a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019fcdef-57dd-78c8-8a75-cdd33af56654" xlink:to="loc_srt_AffiliatedEntityMember_019fcdef-57dd-715d-965f-fc0c8d44266a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7ef2-a44a-762fcda3be46" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019fcdef-57dd-77d6-99df-19a3a14c46f6" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7ef2-a44a-762fcda3be46" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7ef2-a44a-762fcda3be46_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7ef2-a44a-762fcda3be46" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7ef2-a44a-762fcda3be46_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7272-98e0-c236dbe7b555" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7ef2-a44a-762fcda3be46" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7272-98e0-c236dbe7b555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeInc.Member_019fcdef-57dd-794d-94ed-b1eb7b6e62fd" xlink:href="lmnd-20260930.xsd#lmnd_LemonadeInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7272-98e0-c236dbe7b555" xlink:to="loc_lmnd_LemonadeInc.Member_019fcdef-57dd-794d-94ed-b1eb7b6e62fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019fcdef-57dd-7c85-a638-61d02902d7e4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019fcdef-57dd-77d6-99df-19a3a14c46f6" xlink:to="loc_dei_LegalEntityAxis_019fcdef-57dd-7c85-a638-61d02902d7e4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019fcdef-57dd-7c85-a638-61d02902d7e4_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019fcdef-57dd-7c85-a638-61d02902d7e4" xlink:to="loc_dei_EntityDomain_019fcdef-57dd-7c85-a638-61d02902d7e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019fcdef-57dd-7f88-8f84-9be1e1663bcb" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019fcdef-57dd-7c85-a638-61d02902d7e4" xlink:to="loc_dei_EntityDomain_019fcdef-57dd-7f88-8f84-9be1e1663bcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeFoundationMember_019fcdef-57dd-7fa1-8164-076438243e61" xlink:href="lmnd-20260930.xsd#lmnd_LemonadeFoundationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019fcdef-57dd-7f88-8f84-9be1e1663bcb" xlink:to="loc_lmnd_LemonadeFoundationMember_019fcdef-57dd-7fa1-8164-076438243e61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019fcdef-57dd-7fc1-944f-fc798cc01c6a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019fcdef-57dd-77d6-99df-19a3a14c46f6" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019fcdef-57dd-7fc1-944f-fc798cc01c6a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fcdef-57dd-7fc1-944f-fc798cc01c6a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fcdef-57dd-7fc1-944f-fc798cc01c6a" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fcdef-57dd-7fc1-944f-fc798cc01c6a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fcdef-57dd-7f43-9d74-76ff563d1602" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fcdef-57dd-7fc1-944f-fc798cc01c6a" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fcdef-57dd-7f43-9d74-76ff563d1602" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_OmnibusAgreementMember_019fcdef-57dd-79f9-a498-fa223295310b" xlink:href="lmnd-20260930.xsd#lmnd_OmnibusAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fcdef-57dd-7f43-9d74-76ff563d1602" xlink:to="loc_lmnd_OmnibusAgreementMember_019fcdef-57dd-79f9-a498-fa223295310b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-76d9-93c6-924cc7bfbd12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019fcdef-57dd-77d6-99df-19a3a14c46f6" xlink:to="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-76d9-93c6-924cc7bfbd12" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-76d9-93c6-924cc7bfbd12_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-76d9-93c6-924cc7bfbd12" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-76d9-93c6-924cc7bfbd12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-766d-ac02-ad2a324f3382" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-76d9-93c6-924cc7bfbd12" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-766d-ac02-ad2a324f3382" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019fcdef-57dd-737c-aabf-1fce25c901e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-766d-ac02-ad2a324f3382" xlink:to="loc_us-gaap_WarrantMember_019fcdef-57dd-737c-aabf-1fce25c901e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019fcdef-57dd-7f4b-aff0-ebeaace82b06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019fcdef-57dd-7f4b-aff0-ebeaace82b06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019fcdef-57dd-7015-a3ea-0f27eb0531ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019fcdef-57dd-7015-a3ea-0f27eb0531ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019fcdef-57dd-7c17-a321-8e41c717b4c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_CommonStockSharesIssued_019fcdef-57dd-7c17-a321-8e41c717b4c9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019fcdef-57dd-7f80-8aa1-cbcaf9071c8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019fcdef-57dd-7f80-8aa1-cbcaf9071c8a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution_019fcdef-57dd-771e-94a3-3530337ae2b8" xlink:href="lmnd-20260930.xsd#lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution_019fcdef-57dd-771e-94a3-3530337ae2b8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalanceShares_019fcdef-57dd-7d75-821b-f87c2fbdeab7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentOwnedBalanceShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_InvestmentOwnedBalanceShares_019fcdef-57dd-7d75-821b-f87c2fbdeab7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019fcdef-57dd-78e1-aeb8-7a171422d7a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019fcdef-57dd-78e1-aeb8-7a171422d7a8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019fcdef-57dd-7673-a21b-f84d18abe0b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019fcdef-57dd-7673-a21b-f84d18abe0b9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019fcdef-57dd-76d7-99b8-43682f9e6259" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_PreferredStockSharesIssued_019fcdef-57dd-76d7-99b8-43682f9e6259" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019fcdef-57dd-713c-a86f-77f2df07aee8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019fcdef-57dd-713c-a86f-77f2df07aee8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fcdef-57dd-76d5-a4da-111413fdb44b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fcdef-57dd-76d5-a4da-111413fdb44b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fcdef-57dd-7257-bfd6-01ff2bc019f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fcdef-57dd-7257-bfd6-01ff2bc019f1" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019fcdef-57dd-75a7-b13a-e7ba506b08e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019fcdef-57dd-75a7-b13a-e7ba506b08e7" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled_019fcdef-57dd-72ff-9796-2ef2573ee4bf" xlink:href="lmnd-20260930.xsd#lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019fcdef-57dd-77a5-bffe-2bed97579c53" xlink:to="loc_lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled_019fcdef-57dd-72ff-9796-2ef2573ee4bf" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/StockbasedCompensationAdditionalInformationDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#StockbasedCompensationAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/StockbasedCompensationAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-78ba-b6e7-2986269d1e1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-78ba-b6e7-2986269d1e1e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019fcdef-57dd-7df1-a76d-0c6f8539f898" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-78ba-b6e7-2986269d1e1e" xlink:to="loc_us-gaap_PlanNameAxis_019fcdef-57dd-7df1-a76d-0c6f8539f898" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019fcdef-57dd-7df1-a76d-0c6f8539f898_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019fcdef-57dd-7df1-a76d-0c6f8539f898" xlink:to="loc_us-gaap_PlanNameDomain_019fcdef-57dd-7df1-a76d-0c6f8539f898_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019fcdef-57dd-7736-a668-07c16f0a3927" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019fcdef-57dd-7df1-a76d-0c6f8539f898" xlink:to="loc_us-gaap_PlanNameDomain_019fcdef-57dd-7736-a668-07c16f0a3927" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_IncentiveCompensationPlan2020Member_019fcdef-57dd-7bf9-ad8f-b93af2e3b501" xlink:href="lmnd-20260930.xsd#lmnd_IncentiveCompensationPlan2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019fcdef-57dd-7736-a668-07c16f0a3927" xlink:to="loc_lmnd_IncentiveCompensationPlan2020Member_019fcdef-57dd-7bf9-ad8f-b93af2e3b501" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_EmployeeStockPurchasePlan2020Member_019fcdef-57dd-7b9e-808c-c3095f36ae4e" xlink:href="lmnd-20260930.xsd#lmnd_EmployeeStockPurchasePlan2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019fcdef-57dd-7736-a668-07c16f0a3927" xlink:to="loc_lmnd_EmployeeStockPurchasePlan2020Member_019fcdef-57dd-7b9e-808c-c3095f36ae4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_IncentiveShareOptionPlan2015Member_019fcdef-57dd-725e-8c5d-fef571034f92" xlink:href="lmnd-20260930.xsd#lmnd_IncentiveShareOptionPlan2015Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019fcdef-57dd-7736-a668-07c16f0a3927" xlink:to="loc_lmnd_IncentiveShareOptionPlan2015Member_019fcdef-57dd-725e-8c5d-fef571034f92" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_IncentiveStockPlan2021Member_019fcdef-57dd-74ef-94d9-87a6e5400f0a" xlink:href="lmnd-20260930.xsd#lmnd_IncentiveStockPlan2021Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019fcdef-57dd-7736-a668-07c16f0a3927" xlink:to="loc_lmnd_IncentiveStockPlan2021Member_019fcdef-57dd-74ef-94d9-87a6e5400f0a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019fcdef-57dd-7f41-8dbd-3d2037a7e23e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-78ba-b6e7-2986269d1e1e" xlink:to="loc_srt_TitleOfIndividualAxis_019fcdef-57dd-7f41-8dbd-3d2037a7e23e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019fcdef-57dd-7f41-8dbd-3d2037a7e23e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019fcdef-57dd-7f41-8dbd-3d2037a7e23e" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019fcdef-57dd-7f41-8dbd-3d2037a7e23e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019fcdef-57dd-7b2b-ba36-d5367a6a541d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019fcdef-57dd-7f41-8dbd-3d2037a7e23e" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019fcdef-57dd-7b2b-ba36-d5367a6a541d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ChiefExecutiveOfficerAndPresidentMember_019fcdef-57dd-789b-bba5-ddcada7a3863" xlink:href="lmnd-20260930.xsd#lmnd_ChiefExecutiveOfficerAndPresidentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019fcdef-57dd-7b2b-ba36-d5367a6a541d" xlink:to="loc_lmnd_ChiefExecutiveOfficerAndPresidentMember_019fcdef-57dd-789b-bba5-ddcada7a3863" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7c8c-ab9e-45cf7866b041" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-78ba-b6e7-2986269d1e1e" xlink:to="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7c8c-ab9e-45cf7866b041" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7c8c-ab9e-45cf7866b041_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7c8c-ab9e-45cf7866b041" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7c8c-ab9e-45cf7866b041_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7861-a3ad-44c472f2d15b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7c8c-ab9e-45cf7866b041" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7861-a3ad-44c472f2d15b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019fcdef-57dd-720a-9e4a-fb0d5e3326e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7861-a3ad-44c472f2d15b" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019fcdef-57dd-720a-9e4a-fb0d5e3326e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019fcdef-57dd-7820-9bef-20ef919b3a30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7861-a3ad-44c472f2d15b" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019fcdef-57dd-7820-9bef-20ef919b3a30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019fcdef-57dd-74a6-be16-e7edd7ccd8d0" xlink:href="lmnd-20260930.xsd#lmnd_RestrictedStockUnitsWithMarketConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7861-a3ad-44c472f2d15b" xlink:to="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019fcdef-57dd-74a6-be16-e7edd7ccd8d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019fcdef-57dd-7d25-b2b5-f36f309bc2bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7861-a3ad-44c472f2d15b" xlink:to="loc_us-gaap_WarrantMember_019fcdef-57dd-7d25-b2b5-f36f309bc2bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019fcdef-57dd-74aa-b3d6-4d5e470bcda9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-78ba-b6e7-2986269d1e1e" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019fcdef-57dd-74aa-b3d6-4d5e470bcda9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fcdef-57dd-74aa-b3d6-4d5e470bcda9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fcdef-57dd-74aa-b3d6-4d5e470bcda9" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fcdef-57dd-74aa-b3d6-4d5e470bcda9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fcdef-57dd-712d-bf7b-96be349fd72a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019fcdef-57dd-74aa-b3d6-4d5e470bcda9" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fcdef-57dd-712d-bf7b-96be349fd72a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_OmnibusAgreementMember_019fcdef-57dd-7e35-99c1-e597c885b265" xlink:href="lmnd-20260930.xsd#lmnd_OmnibusAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019fcdef-57dd-712d-bf7b-96be349fd72a" xlink:to="loc_lmnd_OmnibusAgreementMember_019fcdef-57dd-7e35-99c1-e597c885b265" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019fcdef-57dd-728b-bda5-faedeff37247" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019fcdef-57dd-728b-bda5-faedeff37247" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreasePercentOfSharesOutstanding_019fcdef-57dd-79cb-a62e-257557cd469a" xlink:href="lmnd-20260930.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreasePercentOfSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreasePercentOfSharesOutstanding_019fcdef-57dd-79cb-a62e-257557cd469a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedMaximumNumberOfSharesIssuedUponExercise_019fcdef-57dd-7bf1-9eff-73492f338f69" xlink:href="lmnd-20260930.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedMaximumNumberOfSharesIssuedUponExercise"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedMaximumNumberOfSharesIssuedUponExercise_019fcdef-57dd-7bf1-9eff-73492f338f69" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019fcdef-57dd-7222-97d6-9013f6eb63fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019fcdef-57dd-7222-97d6-9013f6eb63fe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019fcdef-57dd-7bb9-9d63-5c92f96ccdce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019fcdef-57dd-7bb9-9d63-5c92f96ccdce" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAnnualIncrease_019fcdef-57dd-7907-a8c3-9657d2ff6aa7" xlink:href="lmnd-20260930.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAnnualIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAnnualIncrease_019fcdef-57dd-7907-a8c3-9657d2ff6aa7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInSharesReservedForIssuance_019fcdef-57dd-7bff-8744-5c142bd4eb2f" xlink:href="lmnd-20260930.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInSharesReservedForIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInSharesReservedForIssuance_019fcdef-57dd-7bff-8744-5c142bd4eb2f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019fcdef-57dd-7e03-80cc-993c104c6075" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019fcdef-57dd-7e03-80cc-993c104c6075" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsSharesCalledByEachOption_019fcdef-57dd-7bb6-b317-d1f7d12a492d" xlink:href="lmnd-20260930.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsSharesCalledByEachOption"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsSharesCalledByEachOption_019fcdef-57dd-7bb6-b317-d1f7d12a492d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019fcdef-57dd-72d2-a1e2-5b70f03b7ccf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019fcdef-57dd-72d2-a1e2-5b70f03b7ccf" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019fcdef-57dd-77a1-ba47-a1bfa60ec058" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019fcdef-57dd-77a1-ba47-a1bfa60ec058" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019fcdef-57dd-7685-b41e-6c62abdc6d13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019fcdef-57dd-7685-b41e-6c62abdc6d13" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019fcdef-57dd-7722-9afc-7d4a98620c0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019fcdef-57dd-7722-9afc-7d4a98620c0a" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationByShareBasedPaymentAwardMarketConditionThresholdSharePriceMinimum_019fcdef-57dd-7820-8e21-a6bc6fe632e3" xlink:href="lmnd-20260930.xsd#lmnd_ShareBasedCompensationByShareBasedPaymentAwardMarketConditionThresholdSharePriceMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_lmnd_ShareBasedCompensationByShareBasedPaymentAwardMarketConditionThresholdSharePriceMinimum_019fcdef-57dd-7820-8e21-a6bc6fe632e3" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementConsecutiveTradingDaysStockPriceAtOrAboveThreshold_019fcdef-57dd-79d8-9454-46b1b8611c45" xlink:href="lmnd-20260930.xsd#lmnd_ShareBasedCompensationArrangementConsecutiveTradingDaysStockPriceAtOrAboveThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_lmnd_ShareBasedCompensationArrangementConsecutiveTradingDaysStockPriceAtOrAboveThreshold_019fcdef-57dd-79d8-9454-46b1b8611c45" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardMarketConditionMeasurementPeriod_019fcdef-57dd-7d04-bbf8-116c04376c03" xlink:href="lmnd-20260930.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardMarketConditionMeasurementPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardMarketConditionMeasurementPeriod_019fcdef-57dd-7d04-bbf8-116c04376c03" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue_019fcdef-57dd-7ea9-9380-cddb711004b3" xlink:href="lmnd-20260930.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue_019fcdef-57dd-7ea9-9380-cddb711004b3" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019fcdef-57dd-7f99-8976-06c6257dd285" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019fcdef-57dd-7f99-8976-06c6257dd285" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fcdef-57dd-74bb-b6c9-b0b1aad17120" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fcdef-57dd-74bb-b6c9-b0b1aad17120" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019fcdef-57dd-7ed3-9a04-02224edaafa3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019fcdef-57dd-7ed3-9a04-02224edaafa3" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019fcdef-57dd-7d53-8d0c-0c446f4e28a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019fcdef-57dd-7d53-8d0c-0c446f4e28a0" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fcdef-57dd-7455-9582-ac4181e26cc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fcdef-57dd-7455-9582-ac4181e26cc5" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019fcdef-57dd-7ab0-a83c-166a2188ee95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019fcdef-57dd-7ab0-a83c-166a2188ee95" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedNumber_019fcdef-57dd-755c-8d49-934b9774c77f" xlink:href="lmnd-20260930.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedNumber_019fcdef-57dd-755c-8d49-934b9774c77f" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled_019fcdef-57dd-70df-854b-987ba7913e25" xlink:href="lmnd-20260930.xsd#lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-795a-8047-bdb558d4f253" xlink:to="loc_lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled_019fcdef-57dd-70df-854b-987ba7913e25" xlink:type="arc" order="24"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/StockbasedCompensationFairValueAssumptionsDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#StockbasedCompensationFairValueAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/StockbasedCompensationFairValueAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-789a-94b0-df46357f4dca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-759a-99e9-cc5d4ec86de4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-789a-94b0-df46357f4dca" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-759a-99e9-cc5d4ec86de4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-79e3-91e6-66ccccce1b57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-759a-99e9-cc5d4ec86de4" xlink:to="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-79e3-91e6-66ccccce1b57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-79e3-91e6-66ccccce1b57_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-79e3-91e6-66ccccce1b57" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-79e3-91e6-66ccccce1b57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7a57-8b05-90579b7bb115" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-79e3-91e6-66ccccce1b57" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7a57-8b05-90579b7bb115" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019fcdef-57dd-74d9-8c0a-2f86a31bc6c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7a57-8b05-90579b7bb115" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019fcdef-57dd-74d9-8c0a-2f86a31bc6c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019fcdef-57dd-7060-b056-155d5f173031" xlink:href="lmnd-20260930.xsd#lmnd_RestrictedStockUnitsWithMarketConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7a57-8b05-90579b7bb115" xlink:to="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019fcdef-57dd-7060-b056-155d5f173031" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019fcdef-57dd-76be-8d81-68241a77bab8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-789a-94b0-df46357f4dca" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019fcdef-57dd-76be-8d81-68241a77bab8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019fcdef-57dd-7a75-9eaf-ba2ee8f81a61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-789a-94b0-df46357f4dca" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019fcdef-57dd-7a75-9eaf-ba2ee8f81a61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019fcdef-57dd-75fd-afd3-9b718fada293" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-789a-94b0-df46357f4dca" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019fcdef-57dd-75fd-afd3-9b718fada293" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019fcdef-57dd-7baa-9732-aaed251dd9d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-789a-94b0-df46357f4dca" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019fcdef-57dd-7baa-9732-aaed251dd9d7" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/StockbasedCompensationRestrictedStockUnitsActivityDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#StockbasedCompensationRestrictedStockUnitsActivityDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/StockbasedCompensationRestrictedStockUnitsActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-7ab2-8096-3db33384c3b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-7fb8-baae-78ab8402758f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-7ab2-8096-3db33384c3b7" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-7fb8-baae-78ab8402758f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7ec7-988f-e9e98d7089ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-7fb8-baae-78ab8402758f" xlink:to="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7ec7-988f-e9e98d7089ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7ec7-988f-e9e98d7089ed_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7ec7-988f-e9e98d7089ed" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7ec7-988f-e9e98d7089ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-75ec-9910-8210a2dc358a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7ec7-988f-e9e98d7089ed" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-75ec-9910-8210a2dc358a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019fcdef-57dd-75a7-ade6-2411d8834b7b" xlink:href="lmnd-20260930.xsd#lmnd_RestrictedStockUnitsWithServiceConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-75ec-9910-8210a2dc358a" xlink:to="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019fcdef-57dd-75a7-ade6-2411d8834b7b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019fcdef-57dd-73de-bd11-9c991af05036" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-7ab2-8096-3db33384c3b7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019fcdef-57dd-73de-bd11-9c991af05036" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019fcdef-57dd-7c96-8f8f-7912ff6971d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019fcdef-57dd-73de-bd11-9c991af05036" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019fcdef-57dd-7c96-8f8f-7912ff6971d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019fcdef-57dd-7b85-9d0f-ce39ecfd2648" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019fcdef-57dd-73de-bd11-9c991af05036" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019fcdef-57dd-7b85-9d0f-ce39ecfd2648" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019fcdef-57dd-7f95-8024-d53eb8326f7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019fcdef-57dd-73de-bd11-9c991af05036" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019fcdef-57dd-7f95-8024-d53eb8326f7b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019fcdef-57dd-7c3d-be15-721340a55370" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019fcdef-57dd-73de-bd11-9c991af05036" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019fcdef-57dd-7c3d-be15-721340a55370" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019fcdef-57dd-7fa0-aec4-f6b8cd24c95f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcdef-57dd-730b-ba38-7d8b8d292735" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-7ab2-8096-3db33384c3b7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcdef-57dd-730b-ba38-7d8b8d292735" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019fcdef-57dd-7ca3-82d1-e173485dc4d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcdef-57dd-730b-ba38-7d8b8d292735" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019fcdef-57dd-7ca3-82d1-e173485dc4d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019fcdef-57dd-7bca-ab4d-52a4e03ec780" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcdef-57dd-730b-ba38-7d8b8d292735" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019fcdef-57dd-7bca-ab4d-52a4e03ec780" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019fcdef-57dd-75ae-9b67-1ff053dce6aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcdef-57dd-730b-ba38-7d8b8d292735" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019fcdef-57dd-75ae-9b67-1ff053dce6aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019fcdef-57dd-7fd4-b81d-21a7a5f64690" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019fcdef-57dd-730b-ba38-7d8b8d292735" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019fcdef-57dd-7fd4-b81d-21a7a5f64690" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019fcdef-57dd-7c70-8c11-9389d86a0460" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/StockbasedCompensationStockbasedCompensationExpenseDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#StockbasedCompensationStockbasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/StockbasedCompensationStockbasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-7c26-99a7-1ff7395a4509" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-7132-b15e-d599232301f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-7c26-99a7-1ff7395a4509" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-7132-b15e-d599232301f2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fcdef-57dd-79ec-97ec-96e7c7e33611" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-7132-b15e-d599232301f2" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fcdef-57dd-79ec-97ec-96e7c7e33611" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7710-adcd-19a6e35dd740" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-7132-b15e-d599232301f2" xlink:to="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7710-adcd-19a6e35dd740" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7710-adcd-19a6e35dd740_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7710-adcd-19a6e35dd740" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7710-adcd-19a6e35dd740_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7710-adcd-19a6e35dd740" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019fcdef-57dd-7311-8a36-bc4d4e2d0dc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019fcdef-57dd-7311-8a36-bc4d4e2d0dc3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019fcdef-57dd-7f53-9e6a-f1bada259915" xlink:href="lmnd-20260930.xsd#lmnd_RestrictedStockUnitsWithServiceConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:to="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019fcdef-57dd-7f53-9e6a-f1bada259915" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019fcdef-57dd-7636-9fcc-ee82078c3d45" xlink:href="lmnd-20260930.xsd#lmnd_RestrictedStockUnitsWithMarketConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:to="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019fcdef-57dd-7636-9fcc-ee82078c3d45" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019fcdef-57dd-78c4-bd42-4405fd3402ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:to="loc_us-gaap_WarrantMember_019fcdef-57dd-78c4-bd42-4405fd3402ca" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fcdef-57dd-7cec-be5c-5b78b53e97fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-7c26-99a7-1ff7395a4509" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fcdef-57dd-7cec-be5c-5b78b53e97fd" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/StockbasedCompensationStockbasedCompensationExpenseDetails_1" xlink:type="simple" xlink:href="lmnd-20260930.xsd#StockbasedCompensationStockbasedCompensationExpenseDetails_1"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/StockbasedCompensationStockbasedCompensationExpenseDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-7c26-99a7-1ff7395a4509" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-7132-b15e-d599232301f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-7c26-99a7-1ff7395a4509" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-7132-b15e-d599232301f2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7710-adcd-19a6e35dd740" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fcdef-57dd-7132-b15e-d599232301f2" xlink:to="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7710-adcd-19a6e35dd740" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7710-adcd-19a6e35dd740_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7710-adcd-19a6e35dd740" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-7710-adcd-19a6e35dd740_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019fcdef-57dd-7710-adcd-19a6e35dd740" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019fcdef-57dd-7311-8a36-bc4d4e2d0dc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019fcdef-57dd-7311-8a36-bc4d4e2d0dc3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019fcdef-57dd-7f53-9e6a-f1bada259915" xlink:href="lmnd-20260930.xsd#lmnd_RestrictedStockUnitsWithServiceConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:to="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019fcdef-57dd-7f53-9e6a-f1bada259915" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019fcdef-57dd-7636-9fcc-ee82078c3d45" xlink:href="lmnd-20260930.xsd#lmnd_RestrictedStockUnitsWithMarketConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:to="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019fcdef-57dd-7636-9fcc-ee82078c3d45" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019fcdef-57dd-78c4-bd42-4405fd3402ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fcdef-57dd-73c8-b152-12de2198ff61" xlink:to="loc_us-gaap_WarrantMember_019fcdef-57dd-78c4-bd42-4405fd3402ca" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fcdef-57dd-7cec-be5c-5b78b53e97fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fcdef-57dd-7c26-99a7-1ff7395a4509" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fcdef-57dd-7cec-be5c-5b78b53e97fd" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/IncomeTaxesDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#IncomeTaxesDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/IncomeTaxesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardLineItems_019fcdef-57dd-7159-a50d-cf7a180d16b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxCreditCarryforwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardTable_019fcdef-57dd-7106-8a7b-c9401c20a2ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxCreditCarryforwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_019fcdef-57dd-7159-a50d-cf7a180d16b0" xlink:to="loc_us-gaap_TaxCreditCarryforwardTable_019fcdef-57dd-7106-8a7b-c9401c20a2ad" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019fcdef-57dd-7db7-94ed-5c8207170336" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TaxCreditCarryforwardTable_019fcdef-57dd-7106-8a7b-c9401c20a2ad" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019fcdef-57dd-7db7-94ed-5c8207170336" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019fcdef-57dd-7db7-94ed-5c8207170336_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019fcdef-57dd-7db7-94ed-5c8207170336" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019fcdef-57dd-7db7-94ed-5c8207170336_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019fcdef-57dd-74f3-856f-1bae2d72a7da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019fcdef-57dd-7db7-94ed-5c8207170336" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019fcdef-57dd-74f3-856f-1bae2d72a7da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_019fcdef-57dd-7718-8cf9-32c6e539d571" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019fcdef-57dd-74f3-856f-1bae2d72a7da" xlink:to="loc_us-gaap_DomesticCountryMember_019fcdef-57dd-7718-8cf9-32c6e539d571" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAxis_019fcdef-57dd-7c3e-aebf-e16c4f01f572" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxCreditCarryforwardAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TaxCreditCarryforwardTable_019fcdef-57dd-7106-8a7b-c9401c20a2ad" xlink:to="loc_us-gaap_TaxCreditCarryforwardAxis_019fcdef-57dd-7c3e-aebf-e16c4f01f572" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_019fcdef-57dd-7c3e-aebf-e16c4f01f572_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_019fcdef-57dd-7c3e-aebf-e16c4f01f572" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_019fcdef-57dd-7c3e-aebf-e16c4f01f572_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_019fcdef-57dd-7a1f-b53a-a37d325af789" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_019fcdef-57dd-7c3e-aebf-e16c4f01f572" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_019fcdef-57dd-7a1f-b53a-a37d325af789" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CARESActERCProgramMember_019fcdef-57dd-7fca-9690-ce0b39b4cec2" xlink:href="lmnd-20260930.xsd#lmnd_CARESActERCProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardNameDomain_019fcdef-57dd-7a1f-b53a-a37d325af789" xlink:to="loc_lmnd_CARESActERCProgramMember_019fcdef-57dd-7fca-9690-ce0b39b4cec2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019fcdef-57dd-7d7d-9e3c-b75aa6052997" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_019fcdef-57dd-7159-a50d-cf7a180d16b0" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019fcdef-57dd-7d7d-9e3c-b75aa6052997" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefits_019fcdef-57dd-7f5c-8065-9ea607c28936" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrecognizedTaxBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_019fcdef-57dd-7159-a50d-cf7a180d16b0" xlink:to="loc_us-gaap_UnrecognizedTaxBenefits_019fcdef-57dd-7f5c-8065-9ea607c28936" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_019fcdef-57dd-7949-83e4-b1f7fde714e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_019fcdef-57dd-7159-a50d-cf7a180d16b0" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_019fcdef-57dd-7949-83e4-b1f7fde714e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationTaxCredits_019fcdef-57dd-7a30-9540-4368d0fdf00a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxReconciliationTaxCredits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_019fcdef-57dd-7159-a50d-cf7a180d16b0" xlink:to="loc_us-gaap_IncomeTaxReconciliationTaxCredits_019fcdef-57dd-7a30-9540-4368d0fdf00a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/NetLossperShareAntidilutivePotentialCommonSharesDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#NetLossperShareAntidilutivePotentialCommonSharesDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/NetLossperShareAntidilutivePotentialCommonSharesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019fcdef-57dd-7388-9b1d-472f7fac8ecb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019fcdef-57dd-7363-9e25-cd20e2201490" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019fcdef-57dd-7388-9b1d-472f7fac8ecb" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019fcdef-57dd-7363-9e25-cd20e2201490" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fcdef-57dd-727a-bdac-b140645f80b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019fcdef-57dd-7363-9e25-cd20e2201490" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fcdef-57dd-727a-bdac-b140645f80b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcdef-57dd-727a-bdac-b140645f80b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fcdef-57dd-727a-bdac-b140645f80b4" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcdef-57dd-727a-bdac-b140645f80b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcdef-57dd-7274-969c-64d2ba6d2a62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019fcdef-57dd-727a-bdac-b140645f80b4" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcdef-57dd-7274-969c-64d2ba6d2a62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019fcdef-57dd-7210-ad8a-c6050e8c1aa7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcdef-57dd-7274-969c-64d2ba6d2a62" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019fcdef-57dd-7210-ad8a-c6050e8c1aa7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_019fcdef-57dd-7b44-8014-b7a0728d2442" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcdef-57dd-7274-969c-64d2ba6d2a62" xlink:to="loc_us-gaap_RestrictedStockMember_019fcdef-57dd-7b44-8014-b7a0728d2442" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019fcdef-57dd-7c9a-b997-2016dd9c414d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019fcdef-57dd-7274-969c-64d2ba6d2a62" xlink:to="loc_us-gaap_WarrantMember_019fcdef-57dd-7c9a-b997-2016dd9c414d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fcdef-57dd-7c32-b7f7-6200937e6132" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019fcdef-57dd-7363-9e25-cd20e2201490" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fcdef-57dd-7c32-b7f7-6200937e6132" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcdef-57dd-7c32-b7f7-6200937e6132_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcdef-57dd-7c32-b7f7-6200937e6132" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcdef-57dd-7c32-b7f7-6200937e6132_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcdef-57dd-79cc-b1f3-598ba22273b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcdef-57dd-7c32-b7f7-6200937e6132" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcdef-57dd-79cc-b1f3-598ba22273b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_MetromileMember_019fcdef-57dd-7a5e-a347-1cc6b15c4cfa" xlink:href="lmnd-20260930.xsd#lmnd_MetromileMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcdef-57dd-79cc-b1f3-598ba22273b3" xlink:to="loc_lmnd_MetromileMember_019fcdef-57dd-7a5e-a347-1cc6b15c4cfa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019fcdef-57dd-70e7-a57d-6e801ef02b38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019fcdef-57dd-7388-9b1d-472f7fac8ecb" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019fcdef-57dd-70e7-a57d-6e801ef02b38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShareExchangeRatio_019fcdef-57dd-7ca3-994a-624b29ae5d52" xlink:href="lmnd-20260930.xsd#lmnd_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShareExchangeRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019fcdef-57dd-7388-9b1d-472f7fac8ecb" xlink:to="loc_lmnd_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShareExchangeRatio_019fcdef-57dd-7ca3-994a-624b29ae5d52" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/RelatedPartyTransactionsDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#RelatedPartyTransactionsDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/RelatedPartyTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019fcdef-57dd-7914-ad99-2efcf66dbc2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019fcdef-57dd-71ea-81d1-8b73538f8f6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fcdef-57dd-7914-ad99-2efcf66dbc2e" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019fcdef-57dd-71ea-81d1-8b73538f8f6d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fcdef-57dd-7a6b-a9d1-9517cb5bdd1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019fcdef-57dd-71ea-81d1-8b73538f8f6d" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fcdef-57dd-7a6b-a9d1-9517cb5bdd1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fcdef-57dd-7a6b-a9d1-9517cb5bdd1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fcdef-57dd-7a6b-a9d1-9517cb5bdd1f" xlink:to="loc_us-gaap_RelatedPartyDomain_019fcdef-57dd-7a6b-a9d1-9517cb5bdd1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fcdef-57dd-7971-8162-bbd6f054b00e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fcdef-57dd-7a6b-a9d1-9517cb5bdd1f" xlink:to="loc_us-gaap_RelatedPartyDomain_019fcdef-57dd-7971-8162-bbd6f054b00e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019fcdef-57dd-7e7c-9e62-c57a2e42092e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019fcdef-57dd-7971-8162-bbd6f054b00e" xlink:to="loc_us-gaap_RelatedPartyMember_019fcdef-57dd-7e7c-9e62-c57a2e42092e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019fcdef-57dd-77dc-9cd4-783e2fdb0d10" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019fcdef-57dd-71ea-81d1-8b73538f8f6d" xlink:to="loc_srt_CounterpartyNameAxis_019fcdef-57dd-77dc-9cd4-783e2fdb0d10" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fcdef-57dd-77dc-9cd4-783e2fdb0d10_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019fcdef-57dd-77dc-9cd4-783e2fdb0d10" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fcdef-57dd-77dc-9cd4-783e2fdb0d10_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fcdef-57dd-70e0-b54a-c6bd246699be" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019fcdef-57dd-77dc-9cd4-783e2fdb0d10" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fcdef-57dd-70e0-b54a-c6bd246699be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeFoundationMember_019fcdef-57dd-7214-836e-15b2fedd4cb2" xlink:href="lmnd-20260930.xsd#lmnd_LemonadeFoundationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019fcdef-57dd-70e0-b54a-c6bd246699be" xlink:to="loc_lmnd_LemonadeFoundationMember_019fcdef-57dd-7214-836e-15b2fedd4cb2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019fcdef-57dd-7c74-a684-12c3757ed808" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019fcdef-57dd-71ea-81d1-8b73538f8f6d" xlink:to="loc_dei_LegalEntityAxis_019fcdef-57dd-7c74-a684-12c3757ed808" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019fcdef-57dd-7c74-a684-12c3757ed808_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019fcdef-57dd-7c74-a684-12c3757ed808" xlink:to="loc_dei_EntityDomain_019fcdef-57dd-7c74-a684-12c3757ed808_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019fcdef-57dd-71af-9db4-d3dc130fe6d8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019fcdef-57dd-7c74-a684-12c3757ed808" xlink:to="loc_dei_EntityDomain_019fcdef-57dd-71af-9db4-d3dc130fe6d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeFoundationMember_019fcdef-57dd-7bf7-9b31-bb6109299309" xlink:href="lmnd-20260930.xsd#lmnd_LemonadeFoundationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019fcdef-57dd-71af-9db4-d3dc130fe6d8" xlink:to="loc_lmnd_LemonadeFoundationMember_019fcdef-57dd-7bf7-9b31-bb6109299309" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7c87-95c0-7750d72e3e39" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019fcdef-57dd-71ea-81d1-8b73538f8f6d" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7c87-95c0-7750d72e3e39" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7c87-95c0-7750d72e3e39_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7c87-95c0-7750d72e3e39" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7c87-95c0-7750d72e3e39_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7b0f-ab7d-c272beb60331" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fcdef-57dd-7c87-95c0-7750d72e3e39" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7b0f-ab7d-c272beb60331" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeInc.Member_019fcdef-57dd-7139-a486-fa3412d8c78f" xlink:href="lmnd-20260930.xsd#lmnd_LemonadeInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019fcdef-57dd-7b0f-ab7d-c272beb60331" xlink:to="loc_lmnd_LemonadeInc.Member_019fcdef-57dd-7139-a486-fa3412d8c78f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_NumberOfSharedDirectors_019fcdef-57dd-7899-8bb9-465e84a5f6f6" xlink:href="lmnd-20260930.xsd#lmnd_NumberOfSharedDirectors"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fcdef-57dd-7914-ad99-2efcf66dbc2e" xlink:to="loc_lmnd_NumberOfSharedDirectors_019fcdef-57dd-7899-8bb9-465e84a5f6f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution_019fcdef-57dd-7f10-a7b6-33be0a66f31d" xlink:href="lmnd-20260930.xsd#lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fcdef-57dd-7914-ad99-2efcf66dbc2e" xlink:to="loc_lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution_019fcdef-57dd-7f10-a7b6-33be0a66f31d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_StockIssuedDuringPeriodIssuedForCharitableContributionFairValue_019fcdef-57dd-78f2-a68c-688ce7f240f2" xlink:href="lmnd-20260930.xsd#lmnd_StockIssuedDuringPeriodIssuedForCharitableContributionFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fcdef-57dd-7914-ad99-2efcf66dbc2e" xlink:to="loc_lmnd_StockIssuedDuringPeriodIssuedForCharitableContributionFairValue_019fcdef-57dd-78f2-a68c-688ce7f240f2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalanceShares_019fcdef-57dd-7141-8273-590721b75b8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentOwnedBalanceShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fcdef-57dd-7914-ad99-2efcf66dbc2e" xlink:to="loc_us-gaap_InvestmentOwnedBalanceShares_019fcdef-57dd-7141-8273-590721b75b8d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_019fcdef-57dd-7e42-bcb9-a34aaa6d570c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesAndOtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fcdef-57dd-7914-ad99-2efcf66dbc2e" xlink:to="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_019fcdef-57dd-7e42-bcb9-a34aaa6d570c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NontradeReceivables_019fcdef-57dd-7189-aeb5-d6d3df4b5a61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NontradeReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019fcdef-57dd-7914-ad99-2efcf66dbc2e" xlink:to="loc_us-gaap_NontradeReceivables_019fcdef-57dd-7189-aeb5-d6d3df4b5a61" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/CommitmentsandContingenciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_019fcdef-57dd-7e3d-8546-7d322e0ecebc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_019fcdef-57dd-7f51-9d1a-08ba198feb2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fcdef-57dd-7e3d-8546-7d322e0ecebc" xlink:to="loc_us-gaap_LossContingenciesTable_019fcdef-57dd-7f51-9d1a-08ba198feb2d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsByNatureAxis_019fcdef-57dd-70a2-8718-754f27e18305" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GuaranteeObligationsByNatureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019fcdef-57dd-7f51-9d1a-08ba198feb2d" xlink:to="loc_us-gaap_GuaranteeObligationsByNatureAxis_019fcdef-57dd-70a2-8718-754f27e18305" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_019fcdef-57dd-70a2-8718-754f27e18305_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GuaranteeObligationsNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GuaranteeObligationsByNatureAxis_019fcdef-57dd-70a2-8718-754f27e18305" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_019fcdef-57dd-70a2-8718-754f27e18305_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_019fcdef-57dd-7983-86e9-27480bcdcfd9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GuaranteeObligationsNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GuaranteeObligationsByNatureAxis_019fcdef-57dd-70a2-8718-754f27e18305" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_019fcdef-57dd-7983-86e9-27480bcdcfd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyLeaseGuaranteeMember_019fcdef-57dd-7657-9c41-61260a4a4f9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyLeaseGuaranteeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsNatureDomain_019fcdef-57dd-7983-86e9-27480bcdcfd9" xlink:to="loc_us-gaap_PropertyLeaseGuaranteeMember_019fcdef-57dd-7657-9c41-61260a4a4f9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7841-a18b-a2ea6609453a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualOrInfrequentItemAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019fcdef-57dd-7f51-9d1a-08ba198feb2d" xlink:to="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7841-a18b-a2ea6609453a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7841-a18b-a2ea6609453a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualOrInfrequentItemDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7841-a18b-a2ea6609453a" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-7841-a18b-a2ea6609453a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-735e-9d65-a64d4684a708" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualOrInfrequentItemDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_UnusualOrInfrequentItemAxis_019fcdef-57dd-7841-a18b-a2ea6609453a" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-735e-9d65-a64d4684a708" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CaliforniaWildfiresMember_019fcdef-57dd-7acd-8686-19ee8d05c633" xlink:href="lmnd-20260930.xsd#lmnd_CaliforniaWildfiresMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualOrInfrequentItemDomain_019fcdef-57dd-735e-9d65-a64d4684a708" xlink:to="loc_lmnd_CaliforniaWildfiresMember_019fcdef-57dd-7acd-8686-19ee8d05c633" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicDistributionAxis_01a065fd-e646-703e-a8fd-b306f90e0515" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeographicDistributionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019fcdef-57dd-7f51-9d1a-08ba198feb2d" xlink:to="loc_us-gaap_GeographicDistributionAxis_01a065fd-e646-703e-a8fd-b306f90e0515" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicDistributionDomain_01a065fd-e646-703e-a8fd-b306f90e0515_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeographicDistributionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GeographicDistributionAxis_01a065fd-e646-703e-a8fd-b306f90e0515" xlink:to="loc_us-gaap_GeographicDistributionDomain_01a065fd-e646-703e-a8fd-b306f90e0515_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicDistributionDomain_01a065fd-e646-733f-904a-e7fe47aa52b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeographicDistributionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GeographicDistributionAxis_01a065fd-e646-703e-a8fd-b306f90e0515" xlink:to="loc_us-gaap_GeographicDistributionDomain_01a065fd-e646-733f-904a-e7fe47aa52b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_SanFranciscoMember_01a065fe-0b3c-7c6d-b627-1224d71531dc" xlink:href="lmnd-20260930.xsd#lmnd_SanFranciscoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GeographicDistributionDomain_01a065fd-e646-733f-904a-e7fe47aa52b4" xlink:to="loc_lmnd_SanFranciscoMember_01a065fe-0b3c-7c6d-b627-1224d71531dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualAtCarryingValue_019fcdef-57dd-76ce-ab38-c3534239ddf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingencyAccrualAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fcdef-57dd-7e3d-8546-7d322e0ecebc" xlink:to="loc_us-gaap_LossContingencyAccrualAtCarryingValue_019fcdef-57dd-76ce-ab38-c3534239ddf6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsMaximumExposure_019fcdef-57dd-78b8-a974-65dc1d76b0a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GuaranteeObligationsMaximumExposure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fcdef-57dd-7e3d-8546-7d322e0ecebc" xlink:to="loc_us-gaap_GuaranteeObligationsMaximumExposure_019fcdef-57dd-78b8-a974-65dc1d76b0a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AssessmentChargePercentageRecoupmentApproved_019fcdef-57dd-7e58-b72d-a6c61086f440" xlink:href="lmnd-20260930.xsd#lmnd_AssessmentChargePercentageRecoupmentApproved"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fcdef-57dd-7e3d-8546-7d322e0ecebc" xlink:to="loc_lmnd_AssessmentChargePercentageRecoupmentApproved_019fcdef-57dd-7e58-b72d-a6c61086f440" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AssessmentCharge_019fcdef-57dd-780c-af00-7a7791e3992a" xlink:href="lmnd-20260930.xsd#lmnd_AssessmentCharge"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fcdef-57dd-7e3d-8546-7d322e0ecebc" xlink:to="loc_lmnd_AssessmentCharge_019fcdef-57dd-780c-af00-7a7791e3992a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AssessmentChargeRecoupmentApprovedTerm_019fcdef-57dd-7f71-98f9-92b7dbaa7b9f" xlink:href="lmnd-20260930.xsd#lmnd_AssessmentChargeRecoupmentApprovedTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fcdef-57dd-7e3d-8546-7d322e0ecebc" xlink:to="loc_lmnd_AssessmentChargeRecoupmentApprovedTerm_019fcdef-57dd-7f71-98f9-92b7dbaa7b9f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnTerminationOfLease_01a05857-78d9-73bf-a11e-8f7dc32f4219" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnTerminationOfLease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fcdef-57dd-7e3d-8546-7d322e0ecebc" xlink:to="loc_us-gaap_GainLossOnTerminationOfLease_01a05857-78d9-73bf-a11e-8f7dc32f4219" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_OperatingLeasesRightOfUseAssetsDerecognizedDueToModification_01a05857-78d9-7275-ac83-ca1e5de5d189" xlink:href="lmnd-20260930.xsd#lmnd_OperatingLeasesRightOfUseAssetsDerecognizedDueToModification"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fcdef-57dd-7e3d-8546-7d322e0ecebc" xlink:to="loc_lmnd_OperatingLeasesRightOfUseAssetsDerecognizedDueToModification_01a05857-78d9-7275-ac83-ca1e5de5d189" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/SegmentInformationScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#SegmentInformationScheduleofSegmentReportingInformationbySegmentDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/SegmentInformationScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcdef-57dd-7d49-a5a4-a128e18e1599" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcdef-57dd-7d49-a5a4-a128e18e1599" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fcdef-57dd-7913-b25a-60a0983ccab2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcdef-57dd-7d49-a5a4-a128e18e1599" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fcdef-57dd-7913-b25a-60a0983ccab2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fcdef-57dd-7913-b25a-60a0983ccab2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fcdef-57dd-7913-b25a-60a0983ccab2" xlink:to="loc_us-gaap_SegmentDomain_019fcdef-57dd-7913-b25a-60a0983ccab2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fcdef-57dd-7b8a-bb2d-80e4f15df538" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fcdef-57dd-7913-b25a-60a0983ccab2" xlink:to="loc_us-gaap_SegmentDomain_019fcdef-57dd-7b8a-bb2d-80e4f15df538" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReportableSegmentMember_019fcdef-57dd-7d61-9a5e-d217208f84db" xlink:href="lmnd-20260930.xsd#lmnd_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fcdef-57dd-7b8a-bb2d-80e4f15df538" xlink:to="loc_lmnd_ReportableSegmentMember_019fcdef-57dd-7d61-9a5e-d217208f84db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019fcdef-57dd-7a03-a7f9-f414ad7a2cc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcdef-57dd-7d49-a5a4-a128e18e1599" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019fcdef-57dd-7a03-a7f9-f414ad7a2cc3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019fcdef-57dd-7a03-a7f9-f414ad7a2cc3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019fcdef-57dd-7a03-a7f9-f414ad7a2cc3" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019fcdef-57dd-7a03-a7f9-f414ad7a2cc3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019fcdef-57dd-74b3-aefa-2b37e64929d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019fcdef-57dd-7a03-a7f9-f414ad7a2cc3" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019fcdef-57dd-74b3-aefa-2b37e64929d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_019fcdef-57dd-7188-be96-3d91f9fb6f5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019fcdef-57dd-74b3-aefa-2b37e64929d9" xlink:to="loc_us-gaap_DomesticCountryMember_019fcdef-57dd-7188-be96-3d91f9fb6f5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAxis_019fcdef-57dd-7520-9c6c-53735aebc3cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxCreditCarryforwardAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fcdef-57dd-7d49-a5a4-a128e18e1599" xlink:to="loc_us-gaap_TaxCreditCarryforwardAxis_019fcdef-57dd-7520-9c6c-53735aebc3cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_019fcdef-57dd-7520-9c6c-53735aebc3cd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_019fcdef-57dd-7520-9c6c-53735aebc3cd" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_019fcdef-57dd-7520-9c6c-53735aebc3cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_019fcdef-57dd-7301-ba26-f33df1226088" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_019fcdef-57dd-7520-9c6c-53735aebc3cd" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_019fcdef-57dd-7301-ba26-f33df1226088" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CARESActERCProgramMember_019fcdef-57dd-7d4e-aa51-123d823ddb77" xlink:href="lmnd-20260930.xsd#lmnd_CARESActERCProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardNameDomain_019fcdef-57dd-7301-ba26-f33df1226088" xlink:to="loc_lmnd_CARESActERCProgramMember_019fcdef-57dd-7d4e-aa51-123d823ddb77" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019fcdef-57dd-77b9-90aa-0f8d0b11aba5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_Revenues_019fcdef-57dd-77b9-90aa-0f8d0b11aba5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_019fcdef-57dd-728e-b63d-52dd3364f44c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_019fcdef-57dd-728e-b63d-52dd3364f44c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_OtherInsuranceExpense_019fcdef-57dd-765b-822e-e2ba15f5987c" xlink:href="lmnd-20260930.xsd#lmnd_OtherInsuranceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_lmnd_OtherInsuranceExpense_019fcdef-57dd-765b-822e-e2ba15f5987c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_019fcdef-57dd-7a4b-a6c3-bf88d17e0a90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingAndMarketingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_SellingAndMarketingExpense_019fcdef-57dd-7a4b-a6c3-bf88d17e0a90" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdvertisingExpense_019fcdef-57dd-7fda-9389-3847bcefed11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdvertisingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_AdvertisingExpense_019fcdef-57dd-7fda-9389-3847bcefed11" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019fcdef-57dd-7efc-bdc2-7f1f5875a7db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019fcdef-57dd-7efc-bdc2-7f1f5875a7db" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_GeneralAndAdministrativeLessInterestDepreciationAndOtherSegmentIncomeExpenses_019fcdef-57dd-768a-a770-fa4c3ed84161" xlink:href="lmnd-20260930.xsd#lmnd_GeneralAndAdministrativeLessInterestDepreciationAndOtherSegmentIncomeExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_lmnd_GeneralAndAdministrativeLessInterestDepreciationAndOtherSegmentIncomeExpenses_019fcdef-57dd-768a-a770-fa4c3ed84161" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019fcdef-57dd-7c7a-8088-80e6fa25b5bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019fcdef-57dd-7c7a-8088-80e6fa25b5bf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization_019fcdef-57dd-7efa-a025-e0e85c1ce37b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization_019fcdef-57dd-7efa-a025-e0e85c1ce37b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019fcdef-57dd-75c8-87d1-54a3423af351" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019fcdef-57dd-75c8-87d1-54a3423af351" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019fcdef-57dd-71d8-8592-ce801503fbed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019fcdef-57dd-71d8-8592-ce801503fbed" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019fcdef-57dd-7ba2-9442-f301702ca767" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_NetIncomeLoss_019fcdef-57dd-7ba2-9442-f301702ca767" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationTaxCredits_019fcdef-57dd-737d-9ad4-8ac207958a0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxReconciliationTaxCredits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_IncomeTaxReconciliationTaxCredits_019fcdef-57dd-737d-9ad4-8ac207958a0d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnTerminationOfLease_01a0585d-dcaa-7256-a826-41573f132e67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnTerminationOfLease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_GainLossOnTerminationOfLease_01a0585d-dcaa-7256-a826-41573f132e67" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossRelatedToLitigationSettlement_01a0585d-dcaa-709b-a16c-518a9d97004d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossRelatedToLitigationSettlement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_GainLossRelatedToLitigationSettlement_01a0585d-dcaa-709b-a16c-518a9d97004d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherExpenses_019fcdef-57dd-71a0-a7f3-7049ae65cbc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fcdef-57dd-758a-81e2-5980341dd4f9" xlink:to="loc_us-gaap_OtherExpenses_019fcdef-57dd-71a0-a7f3-7049ae65cbc8" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/SegmentInformationScheduleofGrossWrittenPremiumbyStateDetails" xlink:type="simple" xlink:href="lmnd-20260930.xsd#SegmentInformationScheduleofGrossWrittenPremiumbyStateDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/SegmentInformationScheduleofGrossWrittenPremiumbyStateDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_019fcdef-57dd-7039-9c92-d5db29381d8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fcdef-57dd-7004-87f4-bc84b8f2cec6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_019fcdef-57dd-7039-9c92-d5db29381d8b" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fcdef-57dd-7004-87f4-bc84b8f2cec6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019fcdef-57dd-7a01-8257-52471caacdcf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fcdef-57dd-7004-87f4-bc84b8f2cec6" xlink:to="loc_srt_StatementGeographicalAxis_019fcdef-57dd-7a01-8257-52471caacdcf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7a01-8257-52471caacdcf_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019fcdef-57dd-7a01-8257-52471caacdcf" xlink:to="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7a01-8257-52471caacdcf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019fcdef-57dd-7a01-8257-52471caacdcf" xlink:to="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CA_019fcdef-57dd-7e5e-a94d-543713834d06" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_stpr_CA_019fcdef-57dd-7e5e-a94d-543713834d06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_TX_019fcdef-57dd-7c26-a87f-acca8d1660af" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_TX"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_stpr_TX_019fcdef-57dd-7c26-a87f-acca8d1660af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_NY_019fcdef-57dd-7962-9e41-f956e570fcb7" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_NY"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_stpr_NY_019fcdef-57dd-7962-9e41-f956e570fcb7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_WA_019fcdef-57dd-7da1-97f9-5ac7635c2ea0" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_WA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_stpr_WA_019fcdef-57dd-7da1-97f9-5ac7635c2ea0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_IL_019fcdef-57dd-73d1-93ff-748de4162464" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_IL"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_stpr_IL_019fcdef-57dd-73d1-93ff-748de4162464" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CO_019fcdef-57dd-7db0-a61f-8d9e0dbe43ef" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_CO"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_stpr_CO_019fcdef-57dd-7db0-a61f-8d9e0dbe43ef" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_NJ_019fcdef-57dd-7e8f-9a7c-01253e41d015" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_NJ"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_stpr_NJ_019fcdef-57dd-7e8f-9a7c-01253e41d015" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_FL_019fcdef-57dd-7102-a499-98ebd42788de" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_FL"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_stpr_FL_019fcdef-57dd-7102-a499-98ebd42788de" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_PA_019fcdef-57dd-74c3-bcec-cdab5e32b70a" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_PA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_stpr_PA_019fcdef-57dd-74c3-bcec-cdab5e32b70a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_AZ_019fcdef-57dd-7c4a-ad22-53fa3637e3ee" xlink:href="https://xbrl.sec.gov/stpr/2026/stpr-2026.xsd#stpr_AZ"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_stpr_AZ_019fcdef-57dd-7c4a-ad22-53fa3637e3ee" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AllOtherStatesMember_019fcdef-57dd-705f-a07d-2024bfcb89dc" xlink:href="lmnd-20260930.xsd#lmnd_AllOtherStatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_lmnd_AllOtherStatesMember_019fcdef-57dd-705f-a07d-2024bfcb89dc" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019fcdef-57dd-7e7a-be34-9f2c2da3826c" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_country_US_019fcdef-57dd-7e7a-be34-9f2c2da3826c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_EuropeAndUnitedKingdomMember_019fcdef-57dd-7765-a3a8-aca7a4f57854" xlink:href="lmnd-20260930.xsd#lmnd_EuropeAndUnitedKingdomMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019fcdef-57dd-7218-b357-5297f0f69e7f" xlink:to="loc_lmnd_EuropeAndUnitedKingdomMember_019fcdef-57dd-7765-a3a8-aca7a4f57854" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcdef-57dd-7fdb-bd24-1fe49ce21e05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fcdef-57dd-7004-87f4-bc84b8f2cec6" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcdef-57dd-7fdb-bd24-1fe49ce21e05" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcdef-57dd-7fdb-bd24-1fe49ce21e05_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcdef-57dd-7fdb-bd24-1fe49ce21e05" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcdef-57dd-7fdb-bd24-1fe49ce21e05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcdef-57dd-7a32-91e6-780941b257b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019fcdef-57dd-7fdb-bd24-1fe49ce21e05" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcdef-57dd-7a32-91e6-780941b257b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_PremiumsWrittenGrossBenchmarkMember_019fcdef-57dd-7cef-be50-75ce66905f4f" xlink:href="lmnd-20260930.xsd#lmnd_PremiumsWrittenGrossBenchmarkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019fcdef-57dd-7a32-91e6-780941b257b3" xlink:to="loc_lmnd_PremiumsWrittenGrossBenchmarkMember_019fcdef-57dd-7cef-be50-75ce66905f4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcdef-57dd-77d5-a190-92971bb9adba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019fcdef-57dd-7004-87f4-bc84b8f2cec6" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcdef-57dd-77d5-a190-92971bb9adba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fcdef-57dd-77d5-a190-92971bb9adba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcdef-57dd-77d5-a190-92971bb9adba" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fcdef-57dd-77d5-a190-92971bb9adba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019fcdef-57dd-7628-ace4-e047342f6c69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019fcdef-57dd-77d5-a190-92971bb9adba" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019fcdef-57dd-7628-ace4-e047342f6c69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_019fcdef-57dd-7c94-9217-4ab85ca5dbea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeographicConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019fcdef-57dd-7628-ace4-e047342f6c69" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_019fcdef-57dd-7c94-9217-4ab85ca5dbea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PremiumsWrittenGross_019fcdef-57dd-7ec6-9cb9-bf55e1d652c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PremiumsWrittenGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_019fcdef-57dd-7039-9c92-d5db29381d8b" xlink:to="loc_us-gaap_PremiumsWrittenGross_019fcdef-57dd-7ec6-9cb9-bf55e1d652c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019fcdef-57dd-78c9-b8f3-db403fd6d5af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_019fcdef-57dd-7039-9c92-d5db29381d8b" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019fcdef-57dd-78c9-b8f3-db403fd6d5af" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_TimBixbyMember_019fcdef-5877-79a9-9fe0-e63fa28c1a2a" xlink:href="lmnd-20260930.xsd#lmnd_TimBixbyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_lmnd_TimBixbyMember_019fcdef-5877-79a9-9fe0-e63fa28c1a2a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AdinaEcksteinMember_019fcdef-5877-7659-b893-2d7b53f5de3c" xlink:href="lmnd-20260930.xsd#lmnd_AdinaEcksteinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_lmnd_AdinaEcksteinMember_019fcdef-5877-7659-b893-2d7b53f5de3c" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
