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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e45f1-852a-7d6b-84bb-b5ae27fa49ff,g:ce659921-4570-4336-9202-a551d336ac71-->
<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-20260630.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_019e45f1-86e7-7bc6-a5ab-0e9ca43deeee" 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_019e45f1-86e7-7ee9-a727-45b82e8fe289" 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_019e45f1-86e7-7bc6-a5ab-0e9ca43deeee" xlink:to="loc_us-gaap_StatementTable_019e45f1-86e7-7ee9-a727-45b82e8fe289" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e45f1-86e7-70c5-859c-180411c57638" 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_019e45f1-86e7-7ee9-a727-45b82e8fe289" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e45f1-86e7-70c5-859c-180411c57638" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e45f1-86e7-70c5-859c-180411c57638_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_019e45f1-86e7-70c5-859c-180411c57638" xlink:to="loc_us-gaap_EquityComponentDomain_019e45f1-86e7-70c5-859c-180411c57638_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e45f1-86e7-79b7-9603-b0648c58f45c" 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_019e45f1-86e7-70c5-859c-180411c57638" xlink:to="loc_us-gaap_EquityComponentDomain_019e45f1-86e7-79b7-9603-b0648c58f45c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e45f1-86e7-7533-bb61-b67b14d2bf49" 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_019e45f1-86e7-79b7-9603-b0648c58f45c" xlink:to="loc_us-gaap_CommonStockMember_019e45f1-86e7-7533-bb61-b67b14d2bf49" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019e45f1-86e7-786b-b89e-c81359d5b1f0" 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_019e45f1-86e7-79b7-9603-b0648c58f45c" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019e45f1-86e7-786b-b89e-c81359d5b1f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019e45f1-86e7-70ff-ad91-0b7be218e23f" 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_019e45f1-86e7-79b7-9603-b0648c58f45c" xlink:to="loc_us-gaap_RetainedEarningsMember_019e45f1-86e7-70ff-ad91-0b7be218e23f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e45f1-86e7-76e2-86b5-fddc37857ef2" 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_019e45f1-86e7-79b7-9603-b0648c58f45c" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e45f1-86e7-76e2-86b5-fddc37857ef2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e45f1-86e7-7549-b971-7dff4f594130" 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_019e45f1-86e7-7bc6-a5ab-0e9ca43deeee" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e45f1-86e7-7549-b971-7dff4f594130" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e45f1-86e7-7218-a5fc-3078338a5489" 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_019e45f1-86e7-7549-b971-7dff4f594130" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019e45f1-86e7-7218-a5fc-3078338a5489" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e45f1-86e7-71ab-a195-3e6111579448" 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_019e45f1-86e7-7549-b971-7dff4f594130" xlink:to="loc_us-gaap_StockholdersEquity_019e45f1-86e7-71ab-a195-3e6111579448" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAndRestrictedStockUnitsExercisesInPeriod_019e45f1-86e7-734e-94ca-76a228b75051" xlink:href="lmnd-20260630.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAndRestrictedStockUnitsExercisesInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e45f1-86e7-7549-b971-7dff4f594130" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAndRestrictedStockUnitsExercisesInPeriod_019e45f1-86e7-734e-94ca-76a228b75051" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_StockIssuedDuringPeriodValueStockOptionsAndRestrictedStockExercised_019e45f1-86e7-7911-9332-ef913963644e" xlink:href="lmnd-20260630.xsd#lmnd_StockIssuedDuringPeriodValueStockOptionsAndRestrictedStockExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e45f1-86e7-7549-b971-7dff4f594130" xlink:to="loc_lmnd_StockIssuedDuringPeriodValueStockOptionsAndRestrictedStockExercised_019e45f1-86e7-7911-9332-ef913963644e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e45f1-86e7-74b7-9fb3-eae2fe6a5be5" 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_019e45f1-86e7-7549-b971-7dff4f594130" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e45f1-86e7-74b7-9fb3-eae2fe6a5be5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e45f1-86e7-7bf8-ac54-e6834e13a9d7" 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_019e45f1-86e7-7549-b971-7dff4f594130" xlink:to="loc_us-gaap_NetIncomeLoss_019e45f1-86e7-7bf8-ac54-e6834e13a9d7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019e45f1-86e7-7373-905a-0d1f490f56d1" 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_019e45f1-86e7-7549-b971-7dff4f594130" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019e45f1-86e7-7373-905a-0d1f490f56d1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e45f1-86e7-78d8-a156-8cd938d84372" 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_019e45f1-86e7-7a96-9d3c-5e8d491dd225" 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-20260630.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_019e45f1-86e7-75d1-909a-a02f5f3a6cd0" 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_019e45f1-86e7-708f-87ee-4a43c0ed1e56" 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_019e45f1-86e7-75d1-909a-a02f5f3a6cd0" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019e45f1-86e7-708f-87ee-4a43c0ed1e56" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019e45f1-86e7-7083-857b-9d96d0021361" 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_019e45f1-86e7-708f-87ee-4a43c0ed1e56" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019e45f1-86e7-7083-857b-9d96d0021361" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7083-857b-9d96d0021361_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_019e45f1-86e7-7083-857b-9d96d0021361" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7083-857b-9d96d0021361_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7c3f-8e8e-097cadf6d222" 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_019e45f1-86e7-7083-857b-9d96d0021361" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7c3f-8e8e-097cadf6d222" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019e45f1-86e7-7ab6-8cc1-2f93797aa8ff" 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_019e45f1-86e7-7c3f-8e8e-097cadf6d222" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019e45f1-86e7-7ab6-8cc1-2f93797aa8ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019e45f1-86e7-729e-8347-8ef47eba5144" 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_019e45f1-86e7-7c3f-8e8e-097cadf6d222" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019e45f1-86e7-729e-8347-8ef47eba5144" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019e45f1-86e7-7075-82f0-4e3d60a2b3b1" 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_019e45f1-86e7-7c3f-8e8e-097cadf6d222" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019e45f1-86e7-7075-82f0-4e3d60a2b3b1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019e45f1-86e7-7a63-a51b-dc581a6b7dd6" 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_019e45f1-86e7-7c3f-8e8e-097cadf6d222" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019e45f1-86e7-7a63-a51b-dc581a6b7dd6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019e45f1-86e7-70ba-b1b8-ae68e968e87e" 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_019e45f1-86e7-75d1-909a-a02f5f3a6cd0" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019e45f1-86e7-70ba-b1b8-ae68e968e87e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019e45f1-86e7-7c79-bfcb-c0570b95136f" 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_019e45f1-86e7-75d1-909a-a02f5f3a6cd0" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019e45f1-86e7-7c79-bfcb-c0570b95136f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019e45f1-86e7-72b1-8724-8561d7146daa" 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_019e45f1-86e7-75d1-909a-a02f5f3a6cd0" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019e45f1-86e7-72b1-8724-8561d7146daa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019e45f1-86e7-74db-8741-616265c51634" 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_019e45f1-86e7-75d1-909a-a02f5f3a6cd0" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019e45f1-86e7-74db-8741-616265c51634" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/InvestmentsAdditionalInformationDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-77e7-8699-54befec01026" 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_019e45f1-86e7-767a-a22f-80973e322f04" 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_019e45f1-86e7-77e7-8699-54befec01026" xlink:to="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019e45f1-86e7-767a-a22f-80973e322f04" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019e45f1-86e7-751a-8bd8-e8779a88cb3c" 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_019e45f1-86e7-767a-a22f-80973e322f04" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019e45f1-86e7-751a-8bd8-e8779a88cb3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-751a-8bd8-e8779a88cb3c_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_019e45f1-86e7-751a-8bd8-e8779a88cb3c" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-751a-8bd8-e8779a88cb3c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-705a-b5c3-eac0765ee3c2" 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_019e45f1-86e7-751a-8bd8-e8779a88cb3c" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-705a-b5c3-eac0765ee3c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedIncomeSecuritiesMember_019e45f1-86e7-719d-af82-cadb5061240f" 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_019e45f1-86e7-705a-b5c3-eac0765ee3c2" xlink:to="loc_us-gaap_FixedIncomeSecuritiesMember_019e45f1-86e7-719d-af82-cadb5061240f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019e45f1-86e7-73a2-895d-8a300981bb61" 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_019e45f1-86e7-77e7-8699-54befec01026" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019e45f1-86e7-73a2-895d-8a300981bb61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealizedInvestmentGainsLosses_019e45f1-86e7-76f9-b25b-4ab261b90da4" 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_019e45f1-86e7-77e7-8699-54befec01026" xlink:to="loc_us-gaap_RealizedInvestmentGainsLosses_019e45f1-86e7-76f9-b25b-4ab261b90da4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019e45f1-86e7-7e70-9c2d-237dccd09669" 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_019e45f1-86e7-77e7-8699-54befec01026" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019e45f1-86e7-7e70-9c2d-237dccd09669" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019e45f1-86e7-71a7-8bd1-162d9b448819" 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_019e45f1-86e7-77e7-8699-54befec01026" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019e45f1-86e7-71a7-8bd1-162d9b448819" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_019e45f1-86e7-75c2-aa53-d4a24a24b2f1" 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_019e45f1-86e7-77e7-8699-54befec01026" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLosses_019e45f1-86e7-75c2-aa53-d4a24a24b2f1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedInvestments_019e45f1-86e7-78f8-9068-e140a4b3186d" 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_019e45f1-86e7-77e7-8699-54befec01026" xlink:to="loc_us-gaap_RestrictedInvestments_019e45f1-86e7-78f8-9068-e140a4b3186d" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/InvestmentsNetInvestmentIncomeDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-7414-b300-53caa286e984" 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_019e45f1-86e7-7907-a2a4-c8d199512668" 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_019e45f1-86e7-7414-b300-53caa286e984" xlink:to="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019e45f1-86e7-7907-a2a4-c8d199512668" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019e45f1-86e7-7cb2-a859-6f698268d593" 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_019e45f1-86e7-7907-a2a4-c8d199512668" xlink:to="loc_us-gaap_InvestmentTypeAxis_019e45f1-86e7-7cb2-a859-6f698268d593" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e45f1-86e7-7cb2-a859-6f698268d593_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_019e45f1-86e7-7cb2-a859-6f698268d593" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e45f1-86e7-7cb2-a859-6f698268d593_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e45f1-86e7-7a09-8993-4b99e8c3c308" 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_019e45f1-86e7-7cb2-a859-6f698268d593" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e45f1-86e7-7a09-8993-4b99e8c3c308" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsMember_019e45f1-86e7-7802-b281-45bd215f08c7" 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_019e45f1-86e7-7a09-8993-4b99e8c3c308" xlink:to="loc_us-gaap_CashAndCashEquivalentsMember_019e45f1-86e7-7802-b281-45bd215f08c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_019e45f1-86e7-74e3-8660-d0a0a6edd760" 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_019e45f1-86e7-7a09-8993-4b99e8c3c308" xlink:to="loc_us-gaap_DebtSecuritiesMember_019e45f1-86e7-74e3-8660-d0a0a6edd760" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_019e45f1-86e7-7b10-9e5e-ed1e14a33962" 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_019e45f1-86e7-7a09-8993-4b99e8c3c308" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_019e45f1-86e7-7b10-9e5e-ed1e14a33962" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossInvestmentIncomeOperating_019e45f1-86e7-7ee4-a152-da044322bf46" 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_019e45f1-86e7-7414-b300-53caa286e984" xlink:to="loc_us-gaap_GrossInvestmentIncomeOperating_019e45f1-86e7-7ee4-a152-da044322bf46" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInvestmentExpense_019e45f1-86e7-7911-9824-8a1ba31766fb" 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_019e45f1-86e7-7414-b300-53caa286e984" xlink:to="loc_us-gaap_InvestmentIncomeInvestmentExpense_019e45f1-86e7-7911-9824-8a1ba31766fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019e45f1-86e7-7e19-bb92-f06f424abe3e" 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_019e45f1-86e7-7414-b300-53caa286e984" xlink:to="loc_us-gaap_NetInvestmentIncome_019e45f1-86e7-7e19-bb92-f06f424abe3e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/InvestmentsAgingofGrossUnrealizedLossesDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-7ba3-b562-9f6e7dfa56e2" 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_019e45f1-86e7-7357-acce-1262fe5d8b82" 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_019e45f1-86e7-7ba3-b562-9f6e7dfa56e2" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019e45f1-86e7-7357-acce-1262fe5d8b82" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019e45f1-86e7-730c-bde0-6069a04a2e58" 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_019e45f1-86e7-7357-acce-1262fe5d8b82" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019e45f1-86e7-730c-bde0-6069a04a2e58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-730c-bde0-6069a04a2e58_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_019e45f1-86e7-730c-bde0-6069a04a2e58" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-730c-bde0-6069a04a2e58_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7d8b-a077-db04919df061" 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_019e45f1-86e7-730c-bde0-6069a04a2e58" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7d8b-a077-db04919df061" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019e45f1-86e7-77a5-9f40-d10012c8eb28" 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_019e45f1-86e7-7d8b-a077-db04919df061" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019e45f1-86e7-77a5-9f40-d10012c8eb28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019e45f1-86e7-7dbc-aefc-5b9ce98441dc" 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_019e45f1-86e7-7d8b-a077-db04919df061" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019e45f1-86e7-7dbc-aefc-5b9ce98441dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019e45f1-86e7-7345-9e9d-7249a4065948" 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_019e45f1-86e7-7d8b-a077-db04919df061" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019e45f1-86e7-7345-9e9d-7249a4065948" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019e45f1-86e7-7d5c-b76c-faf22cca0c0c" 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_019e45f1-86e7-7d8b-a077-db04919df061" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019e45f1-86e7-7d5c-b76c-faf22cca0c0c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAbstract_019e45f1-86e7-7768-bfc6-a1d74476bef1" xlink:href="lmnd-20260630.xsd#lmnd_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019e45f1-86e7-7ba3-b562-9f6e7dfa56e2" xlink:to="loc_lmnd_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAbstract_019e45f1-86e7-7768-bfc6-a1d74476bef1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019e45f1-86e7-7410-82a0-367ae10ea0db" 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_019e45f1-86e7-7768-bfc6-a1d74476bef1" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019e45f1-86e7-7410-82a0-367ae10ea0db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019e45f1-86e7-78cb-ba9b-ffaae62f872f" 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_019e45f1-86e7-7768-bfc6-a1d74476bef1" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019e45f1-86e7-78cb-ba9b-ffaae62f872f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019e45f1-86e7-7da1-9d86-742ecc58e14a" 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_019e45f1-86e7-7768-bfc6-a1d74476bef1" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019e45f1-86e7-7da1-9d86-742ecc58e14a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019e45f1-86e7-7aef-b3d6-03b9d6bed75c" 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_019e45f1-86e7-7ba3-b562-9f6e7dfa56e2" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019e45f1-86e7-7aef-b3d6-03b9d6bed75c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019e45f1-86e7-7e53-8339-693aae3d2b9c" 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_019e45f1-86e7-7aef-b3d6-03b9d6bed75c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019e45f1-86e7-7e53-8339-693aae3d2b9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019e45f1-86e7-7059-867b-ae47489e99c2" 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_019e45f1-86e7-7aef-b3d6-03b9d6bed75c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019e45f1-86e7-7059-867b-ae47489e99c2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_019e45f1-86e7-7b27-b63f-47eddd257e0a" 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_019e45f1-86e7-7aef-b3d6-03b9d6bed75c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_019e45f1-86e7-7b27-b63f-47eddd257e0a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/FairValueMeasurementsFairValueHierarchyforFinancialAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-7c55-b0d5-58cfdefed951" 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_019e45f1-86e7-7205-b16c-7cc212d0a318" 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_019e45f1-86e7-7c55-b0d5-58cfdefed951" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e45f1-86e7-7205-b16c-7cc212d0a318" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e45f1-86e7-7cc9-9170-d414b550e98f" 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_019e45f1-86e7-7205-b16c-7cc212d0a318" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e45f1-86e7-7cc9-9170-d414b550e98f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e45f1-86e7-7cc9-9170-d414b550e98f_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_019e45f1-86e7-7cc9-9170-d414b550e98f" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e45f1-86e7-7cc9-9170-d414b550e98f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e45f1-86e7-74db-887c-e39454c5da38" 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_019e45f1-86e7-7cc9-9170-d414b550e98f" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e45f1-86e7-74db-887c-e39454c5da38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019e45f1-86e7-74db-95c4-ded56df883d9" 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_019e45f1-86e7-74db-887c-e39454c5da38" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019e45f1-86e7-74db-95c4-ded56df883d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019e45f1-86e7-711e-a1a7-c120f0378e55" 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_019e45f1-86e7-74db-887c-e39454c5da38" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019e45f1-86e7-711e-a1a7-c120f0378e55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019e45f1-86e7-7e10-acc0-f2ec87cf46d9" 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_019e45f1-86e7-74db-887c-e39454c5da38" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019e45f1-86e7-7e10-acc0-f2ec87cf46d9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019e45f1-86e7-7251-99e8-40062dbdaed1" 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_019e45f1-86e7-7205-b16c-7cc212d0a318" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019e45f1-86e7-7251-99e8-40062dbdaed1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7251-99e8-40062dbdaed1_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_019e45f1-86e7-7251-99e8-40062dbdaed1" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7251-99e8-40062dbdaed1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7a3e-a03e-71c39357ba66" 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_019e45f1-86e7-7251-99e8-40062dbdaed1" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7a3e-a03e-71c39357ba66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019e45f1-86e7-7301-aaa1-31004782327c" 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_019e45f1-86e7-7a3e-a03e-71c39357ba66" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019e45f1-86e7-7301-aaa1-31004782327c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019e45f1-86e7-74a1-882a-d3f985e22c84" 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_019e45f1-86e7-7a3e-a03e-71c39357ba66" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_019e45f1-86e7-74a1-882a-d3f985e22c84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AssetBackedSecuritiesAndCollateralizedLoanObligationsMember_019fa845-132d-7313-995a-e7778dac81db" xlink:href="lmnd-20260630.xsd#lmnd_AssetBackedSecuritiesAndCollateralizedLoanObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7a3e-a03e-71c39357ba66" xlink:to="loc_lmnd_AssetBackedSecuritiesAndCollateralizedLoanObligationsMember_019fa845-132d-7313-995a-e7778dac81db" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019e45f1-86e7-7353-bb52-12c7ebaa2c22" 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_019e45f1-86e7-7a3e-a03e-71c39357ba66" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019e45f1-86e7-7353-bb52-12c7ebaa2c22" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019e45f1-86e7-7a67-8b5d-66720a9ef0e8" 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_019e45f1-86e7-7a3e-a03e-71c39357ba66" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019e45f1-86e7-7a67-8b5d-66720a9ef0e8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019e45f1-86e7-7279-bd78-7bc52ad070b2" 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_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019e45f1-86e7-7a3e-a03e-71c39357ba66" xlink:to="loc_us-gaap_WarrantMember_019e45f1-86e7-7279-bd78-7bc52ad070b2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019e45f1-86e7-7c02-916c-8223ff9a622d" 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_019e45f1-86e7-7c55-b0d5-58cfdefed951" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019e45f1-86e7-7c02-916c-8223ff9a622d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestments_019e45f1-86e7-7678-a1c8-8cdb29655c21" 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_019e45f1-86e7-7c55-b0d5-58cfdefed951" xlink:to="loc_us-gaap_ShortTermInvestments_019e45f1-86e7-7678-a1c8-8cdb29655c21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019e45f1-86e7-7ac5-b4bd-f474732c7af9" 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_019e45f1-86e7-7c55-b0d5-58cfdefed951" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019e45f1-86e7-7ac5-b4bd-f474732c7af9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019e45f1-86e7-73dc-abef-d8f109903147" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e45f1-86e7-7c55-b0d5-58cfdefed951" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019e45f1-86e7-73dc-abef-d8f109903147" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_WarrantsAndRightsOutstandingFairValueDisclosure_019e45f1-86e7-7e48-be80-7c35d031c47d" xlink:href="lmnd-20260630.xsd#lmnd_WarrantsAndRightsOutstandingFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e45f1-86e7-7c55-b0d5-58cfdefed951" xlink:to="loc_lmnd_WarrantsAndRightsOutstandingFairValueDisclosure_019e45f1-86e7-7e48-be80-7c35d031c47d" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/UnpaidLossandLossAdjustmentExpenseAdditionalInformationDetails" xlink:type="simple" xlink:href="lmnd-20260630.xsd#UnpaidLossandLossAdjustmentExpenseAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/UnpaidLossandLossAdjustmentExpenseAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectsOfReinsuranceLineItems_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" 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_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_EffectsOfReinsuranceTable_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemAxis_019e45f1-86e7-712e-aab6-10a95e4da510" 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_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" xlink:to="loc_us-gaap_UnusualOrInfrequentItemAxis_019e45f1-86e7-712e-aab6-10a95e4da510" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-712e-aab6-10a95e4da510_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_019e45f1-86e7-712e-aab6-10a95e4da510" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-712e-aab6-10a95e4da510_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-7a3a-84eb-fe1c5f97434f" 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_019e45f1-86e7-712e-aab6-10a95e4da510" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-7a3a-84eb-fe1c5f97434f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CaliforniaWildfiresMember_019e45f1-86e7-72f0-8fc3-be6bd9112d70" xlink:href="lmnd-20260630.xsd#lmnd_CaliforniaWildfiresMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-7a3a-84eb-fe1c5f97434f" xlink:to="loc_lmnd_CaliforniaWildfiresMember_019e45f1-86e7-72f0-8fc3-be6bd9112d70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e45f1-86e7-7f89-9282-96837ef39978" 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_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" xlink:to="loc_srt_RangeAxis_019e45f1-86e7-7f89-9282-96837ef39978" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e45f1-86e7-7f89-9282-96837ef39978_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_019e45f1-86e7-7f89-9282-96837ef39978" xlink:to="loc_srt_RangeMember_019e45f1-86e7-7f89-9282-96837ef39978_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e45f1-86e7-7a75-a565-c7fa9559a563" 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_019e45f1-86e7-7f89-9282-96837ef39978" xlink:to="loc_srt_RangeMember_019e45f1-86e7-7a75-a565-c7fa9559a563" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e45f1-86e7-7f42-9038-b95187793dff" 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_019e45f1-86e7-7a75-a565-c7fa9559a563" xlink:to="loc_srt_MaximumMember_019e45f1-86e7-7f42-9038-b95187793dff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fa3f1-8e33-7515-91e6-f99ecdd31cea" xlink:href="lmnd-20260630.xsd#lmnd_ReinsuranceArrangementByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fa3f1-8e33-7515-91e6-f99ecdd31cea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-7515-91e6-f99ecdd31cea_default" xlink:href="lmnd-20260630.xsd#lmnd_ReinsuranceArrangementByTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fa3f1-8e33-7515-91e6-f99ecdd31cea" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-7515-91e6-f99ecdd31cea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-769a-8876-6c57f1ca61a6" xlink:href="lmnd-20260630.xsd#lmnd_ReinsuranceArrangementByTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fa3f1-8e33-7515-91e6-f99ecdd31cea" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-769a-8876-6c57f1ca61a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_MICQuotaShareReinsuranceContractMember_019fa3f1-c7ab-7dcd-851c-4f97424fc943" xlink:href="lmnd-20260630.xsd#lmnd_MICQuotaShareReinsuranceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-769a-8876-6c57f1ca61a6" xlink:to="loc_lmnd_MICQuotaShareReinsuranceContractMember_019fa3f1-c7ab-7dcd-851c-4f97424fc943" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LICQuotaShareReinsuranceContractMember_019fa3f1-e0eb-7646-b8cc-a7ddad50a3b7" xlink:href="lmnd-20260630.xsd#lmnd_LICQuotaShareReinsuranceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-769a-8876-6c57f1ca61a6" xlink:to="loc_lmnd_LICQuotaShareReinsuranceContractMember_019fa3f1-e0eb-7646-b8cc-a7ddad50a3b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019fa3f5-d93a-75dd-a87f-fc026ef24fc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019fa3f5-d93a-75dd-a87f-fc026ef24fc6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019fa3f5-d93a-75dd-a87f-fc026ef24fc6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019fa3f5-d93a-75dd-a87f-fc026ef24fc6" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019fa3f5-d93a-75dd-a87f-fc026ef24fc6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019fa3f5-d93a-7778-8d37-f5f89e95cdd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019fa3f5-d93a-75dd-a87f-fc026ef24fc6" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019fa3f5-d93a-7778-8d37-f5f89e95cdd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019fa3f5-f46d-7811-858b-49b27fc15ca7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019fa3f5-d93a-7778-8d37-f5f89e95cdd5" xlink:to="loc_us-gaap_SubsequentEventMember_019fa3f5-f46d-7811-858b-49b27fc15ca7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceContractAxis_019fa3f8-0ddf-7f9d-8a68-b9b7275415fd" 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_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" xlink:to="loc_us-gaap_ReinsuranceContractAxis_019fa3f8-0ddf-7f9d-8a68-b9b7275415fd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019e45f1-86e7-7a05-949b-cb2fcf589117" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019e45f1-86e7-7a05-949b-cb2fcf589117" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_019e45f1-86e7-782f-b7ce-7b1a8b5ced42" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_019e45f1-86e7-782f-b7ce-7b1a8b5ced42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease_019e45f1-86e7-7eab-97e5-b63fd4987bc0" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease_019e45f1-86e7-7eab-97e5-b63fd4987bc0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage_019e45f1-86e7-74ee-a7f2-a368d05843b9" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage_019e45f1-86e7-74ee-a7f2-a368d05843b9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerEvent_019e45f1-86e7-7b34-bb1e-ee34d505dfdf" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerEvent_019e45f1-86e7-7b34-bb1e-ee34d505dfdf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsurancePerRiskLimitAmount_019e45f1-86e7-7075-91e0-4b5ac0b13907" xlink:href="lmnd-20260630.xsd#lmnd_ReinsurancePerRiskLimitAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_lmnd_ReinsurancePerRiskLimitAmount_019e45f1-86e7-7075-91e0-4b5ac0b13907" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerPolicy_019e45f1-86e7-7c15-9da1-e52d1e28fa96" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerPolicy_019e45f1-86e7-7c15-9da1-e52d1e28fa96" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionPolicyExcessRetentionPercentage_019e45f1-86e7-7e2e-be4e-d23e67040e13" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_ReinsuranceRetentionPolicyExcessRetentionPercentage_019e45f1-86e7-7e2e-be4e-d23e67040e13" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionAmountRetainedPerEvent_019e45f1-86e7-7aed-989a-d457e3150118" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_ReinsuranceRetentionAmountRetainedPerEvent_019e45f1-86e7-7aed-989a-d457e3150118" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_PercentageOfDeferredReinsuranceCedingCommissions_019fa3ea-9d95-79e2-96d5-85ac9cf14c82" xlink:href="lmnd-20260630.xsd#lmnd_PercentageOfDeferredReinsuranceCedingCommissions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_lmnd_PercentageOfDeferredReinsuranceCedingCommissions_019fa3ea-9d95-79e2-96d5-85ac9cf14c82" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/UnpaidLossandLossAdjustmentExpenseAdditionalInformationDetails_1" xlink:type="simple" xlink:href="lmnd-20260630.xsd#UnpaidLossandLossAdjustmentExpenseAdditionalInformationDetails_1"/>
  <link:definitionLink xlink:role="http://lemonade.com/role/UnpaidLossandLossAdjustmentExpenseAdditionalInformationDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectsOfReinsuranceLineItems_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" 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_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_EffectsOfReinsuranceTable_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemAxis_019e45f1-86e7-712e-aab6-10a95e4da510" 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_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" xlink:to="loc_us-gaap_UnusualOrInfrequentItemAxis_019e45f1-86e7-712e-aab6-10a95e4da510" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-712e-aab6-10a95e4da510_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_019e45f1-86e7-712e-aab6-10a95e4da510" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-712e-aab6-10a95e4da510_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-7a3a-84eb-fe1c5f97434f" 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_019e45f1-86e7-712e-aab6-10a95e4da510" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-7a3a-84eb-fe1c5f97434f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CaliforniaWildfiresMember_019e45f1-86e7-72f0-8fc3-be6bd9112d70" xlink:href="lmnd-20260630.xsd#lmnd_CaliforniaWildfiresMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-7a3a-84eb-fe1c5f97434f" xlink:to="loc_lmnd_CaliforniaWildfiresMember_019e45f1-86e7-72f0-8fc3-be6bd9112d70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e45f1-86e7-7f89-9282-96837ef39978" 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_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" xlink:to="loc_srt_RangeAxis_019e45f1-86e7-7f89-9282-96837ef39978" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e45f1-86e7-7f89-9282-96837ef39978_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_019e45f1-86e7-7f89-9282-96837ef39978" xlink:to="loc_srt_RangeMember_019e45f1-86e7-7f89-9282-96837ef39978_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e45f1-86e7-7a75-a565-c7fa9559a563" 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_019e45f1-86e7-7f89-9282-96837ef39978" xlink:to="loc_srt_RangeMember_019e45f1-86e7-7a75-a565-c7fa9559a563" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e45f1-86e7-7f42-9038-b95187793dff" 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_019e45f1-86e7-7a75-a565-c7fa9559a563" xlink:to="loc_srt_MaximumMember_019e45f1-86e7-7f42-9038-b95187793dff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fa3f1-8e33-7515-91e6-f99ecdd31cea" xlink:href="lmnd-20260630.xsd#lmnd_ReinsuranceArrangementByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fa3f1-8e33-7515-91e6-f99ecdd31cea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-7515-91e6-f99ecdd31cea_default" xlink:href="lmnd-20260630.xsd#lmnd_ReinsuranceArrangementByTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fa3f1-8e33-7515-91e6-f99ecdd31cea" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-7515-91e6-f99ecdd31cea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-769a-8876-6c57f1ca61a6" xlink:href="lmnd-20260630.xsd#lmnd_ReinsuranceArrangementByTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeAxis_019fa3f1-8e33-7515-91e6-f99ecdd31cea" xlink:to="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-769a-8876-6c57f1ca61a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_MICQuotaShareReinsuranceContractMember_019fa3f1-c7ab-7dcd-851c-4f97424fc943" xlink:href="lmnd-20260630.xsd#lmnd_MICQuotaShareReinsuranceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-769a-8876-6c57f1ca61a6" xlink:to="loc_lmnd_MICQuotaShareReinsuranceContractMember_019fa3f1-c7ab-7dcd-851c-4f97424fc943" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LICQuotaShareReinsuranceContractMember_019fa3f1-e0eb-7646-b8cc-a7ddad50a3b7" xlink:href="lmnd-20260630.xsd#lmnd_LICQuotaShareReinsuranceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_ReinsuranceArrangementByTypeDomain_019fa3f1-8e33-769a-8876-6c57f1ca61a6" xlink:to="loc_lmnd_LICQuotaShareReinsuranceContractMember_019fa3f1-e0eb-7646-b8cc-a7ddad50a3b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019fa3f5-d93a-75dd-a87f-fc026ef24fc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectsOfReinsuranceTable_019e45f1-86e7-7b9e-a7a6-6dfe808f8336" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019fa3f5-d93a-75dd-a87f-fc026ef24fc6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019fa3f5-d93a-75dd-a87f-fc026ef24fc6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019fa3f5-d93a-75dd-a87f-fc026ef24fc6" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019fa3f5-d93a-75dd-a87f-fc026ef24fc6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019fa3f5-d93a-7778-8d37-f5f89e95cdd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019fa3f5-d93a-75dd-a87f-fc026ef24fc6" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019fa3f5-d93a-7778-8d37-f5f89e95cdd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019fa3f5-f46d-7811-858b-49b27fc15ca7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019fa3f5-d93a-7778-8d37-f5f89e95cdd5" xlink:to="loc_us-gaap_SubsequentEventMember_019fa3f5-f46d-7811-858b-49b27fc15ca7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019e45f1-86e7-7a05-949b-cb2fcf589117" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_019e45f1-86e7-7a05-949b-cb2fcf589117" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_019e45f1-86e7-782f-b7ce-7b1a8b5ced42" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense_019e45f1-86e7-782f-b7ce-7b1a8b5ced42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease_019e45f1-86e7-7eab-97e5-b63fd4987bc0" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease_019e45f1-86e7-7eab-97e5-b63fd4987bc0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage_019e45f1-86e7-74ee-a7f2-a368d05843b9" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage_019e45f1-86e7-74ee-a7f2-a368d05843b9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerEvent_019e45f1-86e7-7b34-bb1e-ee34d505dfdf" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerEvent_019e45f1-86e7-7b34-bb1e-ee34d505dfdf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReinsurancePerRiskLimitAmount_019e45f1-86e7-7075-91e0-4b5ac0b13907" xlink:href="lmnd-20260630.xsd#lmnd_ReinsurancePerRiskLimitAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_lmnd_ReinsurancePerRiskLimitAmount_019e45f1-86e7-7075-91e0-4b5ac0b13907" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerPolicy_019e45f1-86e7-7c15-9da1-e52d1e28fa96" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_ReinsuranceRetentionExcessRetentionAmountReinsuredPerPolicy_019e45f1-86e7-7c15-9da1-e52d1e28fa96" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionPolicyExcessRetentionPercentage_019e45f1-86e7-7e2e-be4e-d23e67040e13" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_ReinsuranceRetentionPolicyExcessRetentionPercentage_019e45f1-86e7-7e2e-be4e-d23e67040e13" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReinsuranceRetentionAmountRetainedPerEvent_019e45f1-86e7-7aed-989a-d457e3150118" 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_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_us-gaap_ReinsuranceRetentionAmountRetainedPerEvent_019e45f1-86e7-7aed-989a-d457e3150118" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_PercentageOfDeferredReinsuranceCedingCommissions_019fa3ea-9d95-79e2-96d5-85ac9cf14c82" xlink:href="lmnd-20260630.xsd#lmnd_PercentageOfDeferredReinsuranceCedingCommissions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectsOfReinsuranceLineItems_019e45f1-86e7-7b17-8dd2-5ad8c7e2a4f8" xlink:to="loc_lmnd_PercentageOfDeferredReinsuranceCedingCommissions_019fa3ea-9d95-79e2-96d5-85ac9cf14c82" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/BorrowingsunderFinancingAgreementDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-7543-a78b-5ecdfdbda26b" 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_019e45f1-86e7-78ae-bc9d-8ebe37e90906" 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_019e45f1-86e7-7543-a78b-5ecdfdbda26b" xlink:to="loc_us-gaap_DebtInstrumentTable_019e45f1-86e7-78ae-bc9d-8ebe37e90906" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e45f1-86e7-7389-a6e7-c2438f7f5324" 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_019e45f1-86e7-78ae-bc9d-8ebe37e90906" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e45f1-86e7-7389-a6e7-c2438f7f5324" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e45f1-86e7-7389-a6e7-c2438f7f5324_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_019e45f1-86e7-7389-a6e7-c2438f7f5324" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e45f1-86e7-7389-a6e7-c2438f7f5324_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e45f1-86e7-71e1-a437-f3d4078d3677" 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_019e45f1-86e7-7389-a6e7-c2438f7f5324" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e45f1-86e7-71e1-a437-f3d4078d3677" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CustomerInvestmentAgreementMember_019e45f1-86e7-7403-ae38-a4f99daf05fc" xlink:href="lmnd-20260630.xsd#lmnd_CustomerInvestmentAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e45f1-86e7-71e1-a437-f3d4078d3677" xlink:to="loc_lmnd_CustomerInvestmentAgreementMember_019e45f1-86e7-7403-ae38-a4f99daf05fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AmendedAndRestatedCustomerInvestmentAgreementMember_019e45f1-86e7-7e05-8376-dac518705175" xlink:href="lmnd-20260630.xsd#lmnd_AmendedAndRestatedCustomerInvestmentAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e45f1-86e7-71e1-a437-f3d4078d3677" xlink:to="loc_lmnd_AmendedAndRestatedCustomerInvestmentAgreementMember_019e45f1-86e7-7e05-8376-dac518705175" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_NewBusinessFinancingAgreementMember_019f1b7e-a2ec-77dd-9e58-d3b06edd6bec" xlink:href="lmnd-20260630.xsd#lmnd_NewBusinessFinancingAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e45f1-86e7-71e1-a437-f3d4078d3677" xlink:to="loc_lmnd_NewBusinessFinancingAgreementMember_019f1b7e-a2ec-77dd-9e58-d3b06edd6bec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019e45f1-86e7-7192-8eb2-156af53c5d1f" 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_019e45f1-86e7-78ae-bc9d-8ebe37e90906" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019e45f1-86e7-7192-8eb2-156af53c5d1f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e45f1-86e7-7192-8eb2-156af53c5d1f_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_019e45f1-86e7-7192-8eb2-156af53c5d1f" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e45f1-86e7-7192-8eb2-156af53c5d1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e45f1-86e7-75a5-a8e4-c86c132a4982" 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_019e45f1-86e7-7192-8eb2-156af53c5d1f" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e45f1-86e7-75a5-a8e4-c86c132a4982" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019e45f1-86e7-77cf-a37d-6f5acec701bb" 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_019e45f1-86e7-75a5-a8e4-c86c132a4982" xlink:to="loc_us-gaap_LineOfCreditMember_019e45f1-86e7-77cf-a37d-6f5acec701bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e45f1-86e7-7d30-a6f9-e53899efbd78" 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_019e45f1-86e7-78ae-bc9d-8ebe37e90906" xlink:to="loc_srt_RangeAxis_019e45f1-86e7-7d30-a6f9-e53899efbd78" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e45f1-86e7-7d30-a6f9-e53899efbd78_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_019e45f1-86e7-7d30-a6f9-e53899efbd78" xlink:to="loc_srt_RangeMember_019e45f1-86e7-7d30-a6f9-e53899efbd78_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e45f1-86e7-75df-99f0-5f323dd1362d" 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_019e45f1-86e7-7d30-a6f9-e53899efbd78" xlink:to="loc_srt_RangeMember_019e45f1-86e7-75df-99f0-5f323dd1362d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e45f1-86e7-7df8-9a14-caab0b76581c" 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_019e45f1-86e7-75df-99f0-5f323dd1362d" xlink:to="loc_srt_MinimumMember_019e45f1-86e7-7df8-9a14-caab0b76581c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e45f1-86e7-79ae-b1e9-70086b5299f4" 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_019e45f1-86e7-75df-99f0-5f323dd1362d" xlink:to="loc_srt_MaximumMember_019e45f1-86e7-79ae-b1e9-70086b5299f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019e45f1-86e7-7c5e-acd5-cd657c0f9e3d" 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_019e45f1-86e7-78ae-bc9d-8ebe37e90906" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019e45f1-86e7-7c5e-acd5-cd657c0f9e3d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-7c5e-acd5-cd657c0f9e3d_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_019e45f1-86e7-7c5e-acd5-cd657c0f9e3d" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-7c5e-acd5-cd657c0f9e3d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-710d-bcff-035b25c6a945" 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_019e45f1-86e7-7c5e-acd5-cd657c0f9e3d" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-710d-bcff-035b25c6a945" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_GCCustomerValueArrangerLLCMember_019e45f1-86e7-7951-8cc9-fcf34e132f1c" xlink:href="lmnd-20260630.xsd#lmnd_GCCustomerValueArrangerLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-710d-bcff-035b25c6a945" xlink:to="loc_lmnd_GCCustomerValueArrangerLLCMember_019e45f1-86e7-7951-8cc9-fcf34e132f1c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtInstrumentFundingPeriodAxis_019f41c4-d9c4-75cd-92cc-7d9fd0494681" xlink:href="lmnd-20260630.xsd#lmnd_DebtInstrumentFundingPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e45f1-86e7-78ae-bc9d-8ebe37e90906" xlink:to="loc_lmnd_DebtInstrumentFundingPeriodAxis_019f41c4-d9c4-75cd-92cc-7d9fd0494681" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtInstrumentFundingPeriodDomain_019f41c4-d9c4-75cd-92cc-7d9fd0494681_default" xlink:href="lmnd-20260630.xsd#lmnd_DebtInstrumentFundingPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_lmnd_DebtInstrumentFundingPeriodAxis_019f41c4-d9c4-75cd-92cc-7d9fd0494681" xlink:to="loc_lmnd_DebtInstrumentFundingPeriodDomain_019f41c4-d9c4-75cd-92cc-7d9fd0494681_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtInstrumentFundingPeriodDomain_019f41c4-d9c4-73e5-a1b9-866f31fbb600" xlink:href="lmnd-20260630.xsd#lmnd_DebtInstrumentFundingPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_lmnd_DebtInstrumentFundingPeriodAxis_019f41c4-d9c4-75cd-92cc-7d9fd0494681" xlink:to="loc_lmnd_DebtInstrumentFundingPeriodDomain_019f41c4-d9c4-73e5-a1b9-866f31fbb600" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtInstrumentFundingPeriodTwoMember_019f41c5-17a4-71e0-b055-763b4965ebe5" xlink:href="lmnd-20260630.xsd#lmnd_DebtInstrumentFundingPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_DebtInstrumentFundingPeriodDomain_019f41c4-d9c4-73e5-a1b9-866f31fbb600" xlink:to="loc_lmnd_DebtInstrumentFundingPeriodTwoMember_019f41c5-17a4-71e0-b055-763b4965ebe5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_DebtInstrumentFundingPeriodOneMember_019f41c5-c18c-7a34-8238-7f5fa7ea7358" xlink:href="lmnd-20260630.xsd#lmnd_DebtInstrumentFundingPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_lmnd_DebtInstrumentFundingPeriodDomain_019f41c4-d9c4-73e5-a1b9-866f31fbb600" xlink:to="loc_lmnd_DebtInstrumentFundingPeriodOneMember_019f41c5-c18c-7a34-8238-7f5fa7ea7358" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019f41c8-2d51-7d72-a0b8-c80c32937e6e" 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_019e45f1-86e7-78ae-bc9d-8ebe37e90906" xlink:to="loc_us-gaap_VariableRateAxis_019f41c8-2d51-7d72-a0b8-c80c32937e6e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019f41c8-2d51-7d72-a0b8-c80c32937e6e_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_019f41c8-2d51-7d72-a0b8-c80c32937e6e" xlink:to="loc_us-gaap_VariableRateDomain_019f41c8-2d51-7d72-a0b8-c80c32937e6e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019f41c8-2d51-7262-9d25-6f7115f50b19" 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_019f41c8-2d51-7d72-a0b8-c80c32937e6e" xlink:to="loc_us-gaap_VariableRateDomain_019f41c8-2d51-7262-9d25-6f7115f50b19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReferencePremiumMember_019f41c8-6f97-73f2-b496-ddf6b1e76739" xlink:href="lmnd-20260630.xsd#lmnd_ReferencePremiumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019f41c8-2d51-7262-9d25-6f7115f50b19" xlink:to="loc_lmnd_ReferencePremiumMember_019f41c8-6f97-73f2-b496-ddf6b1e76739" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ThreeYearU.S.TreasuryBillRateMember_019f41c9-7298-72ac-843f-5e271423a0c2" xlink:href="lmnd-20260630.xsd#lmnd_ThreeYearU.S.TreasuryBillRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019f41c8-2d51-7262-9d25-6f7115f50b19" xlink:to="loc_lmnd_ThreeYearU.S.TreasuryBillRateMember_019f41c9-7298-72ac-843f-5e271423a0c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019e45f1-86e7-7f84-8da2-9b5ddba723c3" 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_019e45f1-86e7-7543-a78b-5ecdfdbda26b" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019e45f1-86e7-7f84-8da2-9b5ddba723c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_019f41c9-f950-7810-a2ce-3cfb21abd07e" 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_019e45f1-86e7-7543-a78b-5ecdfdbda26b" xlink:to="loc_us-gaap_DebtInstrumentTerm_019f41c9-f950-7810-a2ce-3cfb21abd07e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LineOfCreditFacilityAdditionalBorrowingCapacity_019e45f1-86e7-7f63-8608-ce63594e616b" xlink:href="lmnd-20260630.xsd#lmnd_LineOfCreditFacilityAdditionalBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e45f1-86e7-7543-a78b-5ecdfdbda26b" xlink:to="loc_lmnd_LineOfCreditFacilityAdditionalBorrowingCapacity_019e45f1-86e7-7f63-8608-ce63594e616b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_InvestmentInEquitySecuritiesFVNIPercentageOfGrowthSpend_019e45f1-86e7-703d-aa8e-a7a5509783f9" xlink:href="lmnd-20260630.xsd#lmnd_InvestmentInEquitySecuritiesFVNIPercentageOfGrowthSpend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e45f1-86e7-7543-a78b-5ecdfdbda26b" xlink:to="loc_lmnd_InvestmentInEquitySecuritiesFVNIPercentageOfGrowthSpend_019e45f1-86e7-703d-aa8e-a7a5509783f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_InvestmentInEquitySecuritiesFVNIInternalRateOfReturnPercent_019e45f1-86e7-757f-8b84-c3197848b327" xlink:href="lmnd-20260630.xsd#lmnd_InvestmentInEquitySecuritiesFVNIInternalRateOfReturnPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e45f1-86e7-7543-a78b-5ecdfdbda26b" xlink:to="loc_lmnd_InvestmentInEquitySecuritiesFVNIInternalRateOfReturnPercent_019e45f1-86e7-757f-8b84-c3197848b327" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019e45f1-86e7-7265-b9a9-8886e946daca" 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_019e45f1-86e7-7543-a78b-5ecdfdbda26b" xlink:to="loc_us-gaap_LongTermDebt_019e45f1-86e7-7265-b9a9-8886e946daca" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_019e45f1-86e7-7504-96da-c464d94ac371" 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_019e45f1-86e7-7543-a78b-5ecdfdbda26b" xlink:to="loc_us-gaap_InterestExpenseDebt_019e45f1-86e7-7504-96da-c464d94ac371" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LineOfCreditFacilityFundingPercentageOfMonthlyGrowthSpend_019f1c03-4809-79db-9db2-717361477005" xlink:href="lmnd-20260630.xsd#lmnd_LineOfCreditFacilityFundingPercentageOfMonthlyGrowthSpend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e45f1-86e7-7543-a78b-5ecdfdbda26b" xlink:to="loc_lmnd_LineOfCreditFacilityFundingPercentageOfMonthlyGrowthSpend_019f1c03-4809-79db-9db2-717361477005" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LineOfCreditFacilityMaximumBorrowingCapacityPerReferenceCohort_019f1bd3-185e-7dc9-9958-bba712b450c6" xlink:href="lmnd-20260630.xsd#lmnd_LineOfCreditFacilityMaximumBorrowingCapacityPerReferenceCohort"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e45f1-86e7-7543-a78b-5ecdfdbda26b" xlink:to="loc_lmnd_LineOfCreditFacilityMaximumBorrowingCapacityPerReferenceCohort_019f1bd3-185e-7dc9-9958-bba712b450c6" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019f1bf2-3992-710f-9ba0-ddb8caafc2c8" 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_019e45f1-86e7-7543-a78b-5ecdfdbda26b" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019f1bf2-3992-710f-9ba0-ddb8caafc2c8" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/StockholdersEquityDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-7daa-b600-5598277ca07f" 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_019e45f1-86e7-7c7c-b1a7-d16ff703c331" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_019e45f1-86e7-7c7c-b1a7-d16ff703c331" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019e45f1-86e7-71d7-8e5f-ec7ea663f7a7" 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_019e45f1-86e7-7c7c-b1a7-d16ff703c331" xlink:to="loc_srt_CounterpartyNameAxis_019e45f1-86e7-71d7-8e5f-ec7ea663f7a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e45f1-86e7-71d7-8e5f-ec7ea663f7a7_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_019e45f1-86e7-71d7-8e5f-ec7ea663f7a7" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e45f1-86e7-71d7-8e5f-ec7ea663f7a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e45f1-86e7-7dfc-b917-f4481dcc2b38" 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_019e45f1-86e7-71d7-8e5f-ec7ea663f7a7" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e45f1-86e7-7dfc-b917-f4481dcc2b38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeFoundationMember_019e45f1-86e7-709d-9518-8112cca8470b" xlink:href="lmnd-20260630.xsd#lmnd_LemonadeFoundationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e45f1-86e7-7dfc-b917-f4481dcc2b38" xlink:to="loc_lmnd_LemonadeFoundationMember_019e45f1-86e7-709d-9518-8112cca8470b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e45f1-86e7-7ee9-b83e-57a1d4568fc9" 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_019e45f1-86e7-7c7c-b1a7-d16ff703c331" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e45f1-86e7-7ee9-b83e-57a1d4568fc9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e45f1-86e7-7ee9-b83e-57a1d4568fc9_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_019e45f1-86e7-7ee9-b83e-57a1d4568fc9" xlink:to="loc_us-gaap_RelatedPartyDomain_019e45f1-86e7-7ee9-b83e-57a1d4568fc9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e45f1-86e7-79fd-a42a-6d1c6fe04ffa" 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_019e45f1-86e7-7ee9-b83e-57a1d4568fc9" xlink:to="loc_us-gaap_RelatedPartyDomain_019e45f1-86e7-79fd-a42a-6d1c6fe04ffa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_019e45f1-86e7-7235-9483-eebed937b4e9" 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_019e45f1-86e7-79fd-a42a-6d1c6fe04ffa" xlink:to="loc_srt_AffiliatedEntityMember_019e45f1-86e7-7235-9483-eebed937b4e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019e45f1-86e7-7211-ac1d-696d4f8b342d" 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_019e45f1-86e7-7c7c-b1a7-d16ff703c331" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019e45f1-86e7-7211-ac1d-696d4f8b342d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-7211-ac1d-696d4f8b342d_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_019e45f1-86e7-7211-ac1d-696d4f8b342d" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-7211-ac1d-696d4f8b342d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-7457-989c-454b9fe62549" 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_019e45f1-86e7-7211-ac1d-696d4f8b342d" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-7457-989c-454b9fe62549" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeInc.Member_019e45f1-86e7-7d47-b2ef-3feb0134bb4e" xlink:href="lmnd-20260630.xsd#lmnd_LemonadeInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-7457-989c-454b9fe62549" xlink:to="loc_lmnd_LemonadeInc.Member_019e45f1-86e7-7d47-b2ef-3feb0134bb4e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e45f1-86e7-714e-b659-4513cf0af15f" 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_019e45f1-86e7-7c7c-b1a7-d16ff703c331" xlink:to="loc_dei_LegalEntityAxis_019e45f1-86e7-714e-b659-4513cf0af15f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e45f1-86e7-714e-b659-4513cf0af15f_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_019e45f1-86e7-714e-b659-4513cf0af15f" xlink:to="loc_dei_EntityDomain_019e45f1-86e7-714e-b659-4513cf0af15f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e45f1-86e7-7313-ab40-9174da32230c" 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_019e45f1-86e7-714e-b659-4513cf0af15f" xlink:to="loc_dei_EntityDomain_019e45f1-86e7-7313-ab40-9174da32230c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeFoundationMember_019e45f1-86e7-767b-9334-47ae91099788" xlink:href="lmnd-20260630.xsd#lmnd_LemonadeFoundationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e45f1-86e7-7313-ab40-9174da32230c" xlink:to="loc_lmnd_LemonadeFoundationMember_019e45f1-86e7-767b-9334-47ae91099788" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019e45f1-86e7-7f1a-93f8-d3ccbdfcacc0" 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_019e45f1-86e7-7c7c-b1a7-d16ff703c331" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019e45f1-86e7-7f1a-93f8-d3ccbdfcacc0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019e45f1-86e7-7f1a-93f8-d3ccbdfcacc0_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_019e45f1-86e7-7f1a-93f8-d3ccbdfcacc0" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019e45f1-86e7-7f1a-93f8-d3ccbdfcacc0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019e45f1-86e7-78ca-89f9-f84c6055549e" 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_019e45f1-86e7-7f1a-93f8-d3ccbdfcacc0" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019e45f1-86e7-78ca-89f9-f84c6055549e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_OmnibusAgreementMember_019e45f1-86e7-779b-bb0f-4c4321fdb206" xlink:href="lmnd-20260630.xsd#lmnd_OmnibusAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019e45f1-86e7-78ca-89f9-f84c6055549e" xlink:to="loc_lmnd_OmnibusAgreementMember_019e45f1-86e7-779b-bb0f-4c4321fdb206" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-78aa-986c-a6508dc6c94b" 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_019e45f1-86e7-7c7c-b1a7-d16ff703c331" xlink:to="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-78aa-986c-a6508dc6c94b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-78aa-986c-a6508dc6c94b_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_019e45f1-86e7-78aa-986c-a6508dc6c94b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-78aa-986c-a6508dc6c94b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7c71-a637-f8cd8b17d3dd" 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_019e45f1-86e7-78aa-986c-a6508dc6c94b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7c71-a637-f8cd8b17d3dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019e45f1-86e7-7805-aa87-792fa97d10c5" 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_019e45f1-86e7-7c71-a637-f8cd8b17d3dd" xlink:to="loc_us-gaap_WarrantMember_019e45f1-86e7-7805-aa87-792fa97d10c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019e45f1-86e7-7c66-b983-adefeb93d127" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019e45f1-86e7-7c66-b983-adefeb93d127" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019e45f1-86e7-7154-bfd5-1431f264d9c8" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019e45f1-86e7-7154-bfd5-1431f264d9c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019e45f1-86e7-7b6e-bab5-a3821cb333f3" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_CommonStockSharesIssued_019e45f1-86e7-7b6e-bab5-a3821cb333f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e45f1-86e7-778e-9c63-3eeb6ec1df29" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019e45f1-86e7-778e-9c63-3eeb6ec1df29" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution_019e45f1-86e7-719c-8cf2-d3915360701a" xlink:href="lmnd-20260630.xsd#lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution_019e45f1-86e7-719c-8cf2-d3915360701a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalanceShares_019e45f1-86e7-7799-ac5d-787928487464" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_InvestmentOwnedBalanceShares_019e45f1-86e7-7799-ac5d-787928487464" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019e45f1-86e7-791c-9f28-2fa6bfe0c786" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019e45f1-86e7-791c-9f28-2fa6bfe0c786" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019e45f1-86e7-7375-a1e1-92d7b95d1afe" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019e45f1-86e7-7375-a1e1-92d7b95d1afe" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019e45f1-86e7-7d62-8d4c-52a8c8acfea4" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_PreferredStockSharesIssued_019e45f1-86e7-7d62-8d4c-52a8c8acfea4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019e45f1-86e7-7264-a5c3-d3225ed6a46b" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019e45f1-86e7-7264-a5c3-d3225ed6a46b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e45f1-86e7-7522-8cef-4530ec071cc7" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e45f1-86e7-7522-8cef-4530ec071cc7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019e45f1-86e7-7352-a04d-c98b17e65a4b" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019e45f1-86e7-7352-a04d-c98b17e65a4b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019e45f1-86e7-7076-b46d-e82ad373d823" 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_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019e45f1-86e7-7076-b46d-e82ad373d823" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled_019e45f1-86e7-793e-923c-cedb30c1c8b6" xlink:href="lmnd-20260630.xsd#lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_019e45f1-86e7-7daa-b600-5598277ca07f" xlink:to="loc_lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled_019e45f1-86e7-793e-923c-cedb30c1c8b6" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/StockbasedCompensationAdditionalInformationDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" 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_019e45f1-86e7-7ed6-a1a9-338fe18cc6bb" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e45f1-86e7-7ed6-a1a9-338fe18cc6bb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019e45f1-86e7-71b9-9542-bf420c6b0008" 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_019e45f1-86e7-7ed6-a1a9-338fe18cc6bb" xlink:to="loc_us-gaap_PlanNameAxis_019e45f1-86e7-71b9-9542-bf420c6b0008" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019e45f1-86e7-71b9-9542-bf420c6b0008_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_019e45f1-86e7-71b9-9542-bf420c6b0008" xlink:to="loc_us-gaap_PlanNameDomain_019e45f1-86e7-71b9-9542-bf420c6b0008_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019e45f1-86e7-72a4-b999-b70cca646ecd" 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_019e45f1-86e7-71b9-9542-bf420c6b0008" xlink:to="loc_us-gaap_PlanNameDomain_019e45f1-86e7-72a4-b999-b70cca646ecd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_IncentiveCompensationPlan2020Member_019e45f1-86e7-7ded-9e3f-fc29d553a362" xlink:href="lmnd-20260630.xsd#lmnd_IncentiveCompensationPlan2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019e45f1-86e7-72a4-b999-b70cca646ecd" xlink:to="loc_lmnd_IncentiveCompensationPlan2020Member_019e45f1-86e7-7ded-9e3f-fc29d553a362" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_EmployeeStockPurchasePlan2020Member_019e45f1-86e7-76be-a1eb-d43f7d22f295" xlink:href="lmnd-20260630.xsd#lmnd_EmployeeStockPurchasePlan2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019e45f1-86e7-72a4-b999-b70cca646ecd" xlink:to="loc_lmnd_EmployeeStockPurchasePlan2020Member_019e45f1-86e7-76be-a1eb-d43f7d22f295" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_IncentiveShareOptionPlan2015Member_019e45f1-86e7-7f22-8cd0-820e1b667fb8" xlink:href="lmnd-20260630.xsd#lmnd_IncentiveShareOptionPlan2015Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019e45f1-86e7-72a4-b999-b70cca646ecd" xlink:to="loc_lmnd_IncentiveShareOptionPlan2015Member_019e45f1-86e7-7f22-8cd0-820e1b667fb8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_IncentiveStockPlan2021Member_019e45f1-86e7-7c85-a806-e2860d4677e2" xlink:href="lmnd-20260630.xsd#lmnd_IncentiveStockPlan2021Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019e45f1-86e7-72a4-b999-b70cca646ecd" xlink:to="loc_lmnd_IncentiveStockPlan2021Member_019e45f1-86e7-7c85-a806-e2860d4677e2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019e45f1-86e7-7800-8326-5734b4f89b08" 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_019e45f1-86e7-7ed6-a1a9-338fe18cc6bb" xlink:to="loc_srt_TitleOfIndividualAxis_019e45f1-86e7-7800-8326-5734b4f89b08" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019e45f1-86e7-7800-8326-5734b4f89b08_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_019e45f1-86e7-7800-8326-5734b4f89b08" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019e45f1-86e7-7800-8326-5734b4f89b08_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019e45f1-86e7-7758-a469-a9ce0ffdce1f" 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_019e45f1-86e7-7800-8326-5734b4f89b08" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019e45f1-86e7-7758-a469-a9ce0ffdce1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ChiefExecutiveOfficerAndPresidentMember_019e45f1-86e7-7b99-83c8-33f4af85553d" xlink:href="lmnd-20260630.xsd#lmnd_ChiefExecutiveOfficerAndPresidentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019e45f1-86e7-7758-a469-a9ce0ffdce1f" xlink:to="loc_lmnd_ChiefExecutiveOfficerAndPresidentMember_019e45f1-86e7-7b99-83c8-33f4af85553d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-71b1-a64c-f0dfd908383d" 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_019e45f1-86e7-7ed6-a1a9-338fe18cc6bb" xlink:to="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-71b1-a64c-f0dfd908383d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-71b1-a64c-f0dfd908383d_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_019e45f1-86e7-71b1-a64c-f0dfd908383d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-71b1-a64c-f0dfd908383d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7009-963b-9b8f58fdee8d" 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_019e45f1-86e7-71b1-a64c-f0dfd908383d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7009-963b-9b8f58fdee8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019e45f1-86e7-7665-9980-b004bad87562" 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_019e45f1-86e7-7009-963b-9b8f58fdee8d" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019e45f1-86e7-7665-9980-b004bad87562" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019e45f1-86e7-7cb4-bdf1-f1eaa80b9518" 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_019e45f1-86e7-7009-963b-9b8f58fdee8d" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019e45f1-86e7-7cb4-bdf1-f1eaa80b9518" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019e45f1-86e7-7e69-834a-73d248bd77e0" 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_019e45f1-86e7-7009-963b-9b8f58fdee8d" xlink:to="loc_us-gaap_WarrantMember_019e45f1-86e7-7e69-834a-73d248bd77e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019e45f1-86e7-78c3-9152-882c06de1411" xlink:href="lmnd-20260630.xsd#lmnd_RestrictedStockUnitsWithMarketConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7009-963b-9b8f58fdee8d" xlink:to="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019e45f1-86e7-78c3-9152-882c06de1411" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019e45f1-86e7-7af8-bd15-d840cf3cc97d" 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_019e45f1-86e7-7ed6-a1a9-338fe18cc6bb" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019e45f1-86e7-7af8-bd15-d840cf3cc97d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019e45f1-86e7-7af8-bd15-d840cf3cc97d_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_019e45f1-86e7-7af8-bd15-d840cf3cc97d" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019e45f1-86e7-7af8-bd15-d840cf3cc97d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019e45f1-86e7-73cd-8562-5dc7ece3d50e" 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_019e45f1-86e7-7af8-bd15-d840cf3cc97d" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019e45f1-86e7-73cd-8562-5dc7ece3d50e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_OmnibusAgreementMember_019e45f1-86e7-72ad-95d8-937b3ad6181a" xlink:href="lmnd-20260630.xsd#lmnd_OmnibusAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019e45f1-86e7-73cd-8562-5dc7ece3d50e" xlink:to="loc_lmnd_OmnibusAgreementMember_019e45f1-86e7-72ad-95d8-937b3ad6181a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019e45f1-86e7-79d7-b4fa-31c8d1e779fd" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019e45f1-86e7-79d7-b4fa-31c8d1e779fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreasePercentOfSharesOutstanding_019e45f1-86e7-78c8-b91d-f05cdbe1a3cf" xlink:href="lmnd-20260630.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreasePercentOfSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreasePercentOfSharesOutstanding_019e45f1-86e7-78c8-b91d-f05cdbe1a3cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedMaximumNumberOfSharesIssuedUponExercise_019e45f1-86e7-7c96-af46-b65527a53427" xlink:href="lmnd-20260630.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedMaximumNumberOfSharesIssuedUponExercise"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedMaximumNumberOfSharesIssuedUponExercise_019e45f1-86e7-7c96-af46-b65527a53427" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019e45f1-86e7-78e5-82c9-53770f14e1b5" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019e45f1-86e7-78e5-82c9-53770f14e1b5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019e45f1-86e7-75eb-8033-85c7ddc7c29d" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019e45f1-86e7-75eb-8033-85c7ddc7c29d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAnnualIncrease_019e45f1-86e7-7b05-a692-f7af983b6379" xlink:href="lmnd-20260630.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAnnualIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAnnualIncrease_019e45f1-86e7-7b05-a692-f7af983b6379" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInSharesReservedForIssuance_019e45f1-86e7-750a-add1-e4bd2c13d89e" xlink:href="lmnd-20260630.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInSharesReservedForIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInSharesReservedForIssuance_019e45f1-86e7-750a-add1-e4bd2c13d89e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019e45f1-86e7-7da7-8eb1-adfb1f05450e" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019e45f1-86e7-7da7-8eb1-adfb1f05450e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsSharesCalledByEachOption_019e45f1-86e7-77f4-b101-de94191af9be" xlink:href="lmnd-20260630.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsSharesCalledByEachOption"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsSharesCalledByEachOption_019e45f1-86e7-77f4-b101-de94191af9be" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019e45f1-86e7-7804-8ee4-36b2156fbbfc" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019e45f1-86e7-7804-8ee4-36b2156fbbfc" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019e45f1-86e7-7dd0-b477-7b4f5c0e478c" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019e45f1-86e7-7dd0-b477-7b4f5c0e478c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019e45f1-86e7-739d-9536-15159b3b3e5b" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019e45f1-86e7-739d-9536-15159b3b3e5b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e45f1-86e7-7455-96e6-3b36df62f96c" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e45f1-86e7-7455-96e6-3b36df62f96c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationByShareBasedPaymentAwardMarketConditionThresholdSharePriceMinimum_019e45f1-86e7-7903-86dc-9c67625c3e5e" xlink:href="lmnd-20260630.xsd#lmnd_ShareBasedCompensationByShareBasedPaymentAwardMarketConditionThresholdSharePriceMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_lmnd_ShareBasedCompensationByShareBasedPaymentAwardMarketConditionThresholdSharePriceMinimum_019e45f1-86e7-7903-86dc-9c67625c3e5e" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementConsecutiveTradingDaysStockPriceAtOrAboveThreshold_019e45f1-86e7-7cc5-9b60-3df1a3fe5694" xlink:href="lmnd-20260630.xsd#lmnd_ShareBasedCompensationArrangementConsecutiveTradingDaysStockPriceAtOrAboveThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_lmnd_ShareBasedCompensationArrangementConsecutiveTradingDaysStockPriceAtOrAboveThreshold_019e45f1-86e7-7cc5-9b60-3df1a3fe5694" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardMarketConditionMeasurementPeriod_019e45f1-86e7-715d-84ff-7a8164d8fd92" xlink:href="lmnd-20260630.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardMarketConditionMeasurementPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardMarketConditionMeasurementPeriod_019e45f1-86e7-715d-84ff-7a8164d8fd92" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue_019e45f1-86e7-7d3e-b079-6d3cd8f0739e" xlink:href="lmnd-20260630.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue_019e45f1-86e7-7d3e-b079-6d3cd8f0739e" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019e45f1-86e7-77f8-b0a0-30905c24458b" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019e45f1-86e7-77f8-b0a0-30905c24458b" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e45f1-86e7-7d17-af24-cfed9b121220" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e45f1-86e7-7d17-af24-cfed9b121220" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019e45f1-86e7-75d4-bf67-4ff07b554091" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019e45f1-86e7-75d4-bf67-4ff07b554091" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019e45f1-86e7-7e97-bb26-f8b50a6b165a" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019e45f1-86e7-7e97-bb26-f8b50a6b165a" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e45f1-86e7-7c6c-8f95-caaeca1f29ec" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e45f1-86e7-7c6c-8f95-caaeca1f29ec" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e45f1-86e7-7437-b4e3-80bd9ba1427e" 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_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e45f1-86e7-7437-b4e3-80bd9ba1427e" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedNumber_019e45f1-86e7-76ef-a89d-4b14790c41a2" xlink:href="lmnd-20260630.xsd#lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_lmnd_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedNumber_019e45f1-86e7-76ef-a89d-4b14790c41a2" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled_019e45f1-86e7-7ae6-9859-eb1afdec285e" xlink:href="lmnd-20260630.xsd#lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e45f1-86e7-7ff4-a0ae-924e602be2bb" xlink:to="loc_lmnd_ClassOfWarrantOrRightNumberOfWarrantsCancelled_019e45f1-86e7-7ae6-9859-eb1afdec285e" xlink:type="arc" order="24"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/StockbasedCompensationFairValueAssumptionsDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-7189-a877-93a906a8ff36" 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_019e45f1-86e7-756b-946d-f221957e6b8c" 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_019e45f1-86e7-7189-a877-93a906a8ff36" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e45f1-86e7-756b-946d-f221957e6b8c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-7150-9590-d00928f228e6" 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_019e45f1-86e7-756b-946d-f221957e6b8c" xlink:to="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-7150-9590-d00928f228e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7150-9590-d00928f228e6_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_019e45f1-86e7-7150-9590-d00928f228e6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7150-9590-d00928f228e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7cfa-8708-fdfd8005bc79" 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_019e45f1-86e7-7150-9590-d00928f228e6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7cfa-8708-fdfd8005bc79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019e45f1-86e7-7caa-9db1-a2788acc819b" 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_019e45f1-86e7-7cfa-8708-fdfd8005bc79" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019e45f1-86e7-7caa-9db1-a2788acc819b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019e45f1-86e7-7ba3-9ff5-f2ca36a07756" xlink:href="lmnd-20260630.xsd#lmnd_RestrictedStockUnitsWithMarketConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7cfa-8708-fdfd8005bc79" xlink:to="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019e45f1-86e7-7ba3-9ff5-f2ca36a07756" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019e45f1-86e7-7b5d-bbde-3a1775aa6a30" 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_019e45f1-86e7-7189-a877-93a906a8ff36" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019e45f1-86e7-7b5d-bbde-3a1775aa6a30" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019e45f1-86e7-7eb2-a0a3-81bf674efc75" 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_019e45f1-86e7-7189-a877-93a906a8ff36" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019e45f1-86e7-7eb2-a0a3-81bf674efc75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019e45f1-86e7-783f-8793-fe0017305dd1" 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_019e45f1-86e7-7189-a877-93a906a8ff36" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019e45f1-86e7-783f-8793-fe0017305dd1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019e45f1-86e7-7c0c-8797-7ab203478d9b" 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_019e45f1-86e7-7189-a877-93a906a8ff36" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019e45f1-86e7-7c0c-8797-7ab203478d9b" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/StockbasedCompensationRestrictedStockUnitsActivityDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-7c9e-b8fe-cd56a2faed20" 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_019e45f1-86e7-7738-871e-d1225a37ce6f" 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_019e45f1-86e7-7c9e-b8fe-cd56a2faed20" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e45f1-86e7-7738-871e-d1225a37ce6f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-7863-b55f-cd3e043618ab" 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_019e45f1-86e7-7738-871e-d1225a37ce6f" xlink:to="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-7863-b55f-cd3e043618ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7863-b55f-cd3e043618ab_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_019e45f1-86e7-7863-b55f-cd3e043618ab" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7863-b55f-cd3e043618ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-77a1-912c-f8c6e20c328e" 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_019e45f1-86e7-7863-b55f-cd3e043618ab" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-77a1-912c-f8c6e20c328e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019e45f1-86e7-7cf5-b2aa-c2a877de41e9" xlink:href="lmnd-20260630.xsd#lmnd_RestrictedStockUnitsWithServiceConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-77a1-912c-f8c6e20c328e" xlink:to="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019e45f1-86e7-7cf5-b2aa-c2a877de41e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e45f1-86e7-70af-bba3-9bca243672de" 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_019e45f1-86e7-7c9e-b8fe-cd56a2faed20" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e45f1-86e7-70af-bba3-9bca243672de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e45f1-86e7-7d74-8f35-dd80126530cd" 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_019e45f1-86e7-70af-bba3-9bca243672de" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e45f1-86e7-7d74-8f35-dd80126530cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e45f1-86e7-7a8a-9576-ad80dc0b5c42" 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_019e45f1-86e7-70af-bba3-9bca243672de" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e45f1-86e7-7a8a-9576-ad80dc0b5c42" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019e45f1-86e7-7c3d-b3c6-c344be07f9a0" 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_019e45f1-86e7-70af-bba3-9bca243672de" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019e45f1-86e7-7c3d-b3c6-c344be07f9a0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019e45f1-86e7-7577-892c-a79b2ac2aaf6" 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_019e45f1-86e7-70af-bba3-9bca243672de" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019e45f1-86e7-7577-892c-a79b2ac2aaf6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e45f1-86e7-78f4-bbad-51bb3c0e5e6a" 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_019e45f1-86e7-7ff6-8cd2-d56e342c3fc3" 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_019e45f1-86e7-7c9e-b8fe-cd56a2faed20" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e45f1-86e7-7ff6-8cd2-d56e342c3fc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e45f1-86e7-74ae-9901-82a5564dc10e" 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_019e45f1-86e7-7ff6-8cd2-d56e342c3fc3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e45f1-86e7-74ae-9901-82a5564dc10e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e45f1-86e7-74b2-b481-9dff3e1f3d23" 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_019e45f1-86e7-7ff6-8cd2-d56e342c3fc3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e45f1-86e7-74b2-b481-9dff3e1f3d23" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019e45f1-86e7-7b3d-bb4d-68db7fdd42c5" 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_019e45f1-86e7-7ff6-8cd2-d56e342c3fc3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019e45f1-86e7-7b3d-bb4d-68db7fdd42c5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019e45f1-86e7-7765-80d5-9071d924357c" 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_019e45f1-86e7-7ff6-8cd2-d56e342c3fc3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019e45f1-86e7-7765-80d5-9071d924357c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e45f1-86e7-7ad3-bc0f-e961260b521a" 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-20260630.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_019e45f1-86e7-79f6-9772-e22817f3c558" 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_019e45f1-86e7-709d-b28b-7ee34df3703c" 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_019e45f1-86e7-79f6-9772-e22817f3c558" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e45f1-86e7-709d-b28b-7ee34df3703c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019e45f1-86e7-7fa0-aa8e-a7a3475ce0af" 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_019e45f1-86e7-709d-b28b-7ee34df3703c" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019e45f1-86e7-7fa0-aa8e-a7a3475ce0af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-7499-8135-d44dd973b38e" 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_019e45f1-86e7-709d-b28b-7ee34df3703c" xlink:to="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-7499-8135-d44dd973b38e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7499-8135-d44dd973b38e_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_019e45f1-86e7-7499-8135-d44dd973b38e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7499-8135-d44dd973b38e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-753f-8bf9-577b63d4a164" 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_019e45f1-86e7-7499-8135-d44dd973b38e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-753f-8bf9-577b63d4a164" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019e45f1-86e7-726f-a68d-2dfaa8a14df6" 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_019e45f1-86e7-753f-8bf9-577b63d4a164" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019e45f1-86e7-726f-a68d-2dfaa8a14df6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019e45f1-86e7-79b5-acfb-2009719154d0" xlink:href="lmnd-20260630.xsd#lmnd_RestrictedStockUnitsWithServiceConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-753f-8bf9-577b63d4a164" xlink:to="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019e45f1-86e7-79b5-acfb-2009719154d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019e45f1-86e7-7dc4-bcec-e7bc75878bd0" xlink:href="lmnd-20260630.xsd#lmnd_RestrictedStockUnitsWithMarketConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-753f-8bf9-577b63d4a164" xlink:to="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019e45f1-86e7-7dc4-bcec-e7bc75878bd0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019e45f1-86e7-7ce9-a61a-95661ff146b0" 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_019e45f1-86e7-753f-8bf9-577b63d4a164" xlink:to="loc_us-gaap_WarrantMember_019e45f1-86e7-7ce9-a61a-95661ff146b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e45f1-86e7-71e3-b63c-00033ea1cf78" 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_019e45f1-86e7-79f6-9772-e22817f3c558" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e45f1-86e7-71e3-b63c-00033ea1cf78" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/StockbasedCompensationStockbasedCompensationExpenseDetails_1" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-79f6-9772-e22817f3c558" 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_019e45f1-86e7-709d-b28b-7ee34df3703c" 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_019e45f1-86e7-79f6-9772-e22817f3c558" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e45f1-86e7-709d-b28b-7ee34df3703c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-7499-8135-d44dd973b38e" 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_019e45f1-86e7-709d-b28b-7ee34df3703c" xlink:to="loc_us-gaap_AwardTypeAxis_019e45f1-86e7-7499-8135-d44dd973b38e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7499-8135-d44dd973b38e_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_019e45f1-86e7-7499-8135-d44dd973b38e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-7499-8135-d44dd973b38e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-753f-8bf9-577b63d4a164" 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_019e45f1-86e7-7499-8135-d44dd973b38e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-753f-8bf9-577b63d4a164" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019e45f1-86e7-726f-a68d-2dfaa8a14df6" 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_019e45f1-86e7-753f-8bf9-577b63d4a164" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019e45f1-86e7-726f-a68d-2dfaa8a14df6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019e45f1-86e7-79b5-acfb-2009719154d0" xlink:href="lmnd-20260630.xsd#lmnd_RestrictedStockUnitsWithServiceConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-753f-8bf9-577b63d4a164" xlink:to="loc_lmnd_RestrictedStockUnitsWithServiceConditionsMember_019e45f1-86e7-79b5-acfb-2009719154d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019e45f1-86e7-7dc4-bcec-e7bc75878bd0" xlink:href="lmnd-20260630.xsd#lmnd_RestrictedStockUnitsWithMarketConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e45f1-86e7-753f-8bf9-577b63d4a164" xlink:to="loc_lmnd_RestrictedStockUnitsWithMarketConditionsMember_019e45f1-86e7-7dc4-bcec-e7bc75878bd0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019e45f1-86e7-7ce9-a61a-95661ff146b0" 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_019e45f1-86e7-753f-8bf9-577b63d4a164" xlink:to="loc_us-gaap_WarrantMember_019e45f1-86e7-7ce9-a61a-95661ff146b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e45f1-86e7-71e3-b63c-00033ea1cf78" 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_019e45f1-86e7-79f6-9772-e22817f3c558" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e45f1-86e7-71e3-b63c-00033ea1cf78" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/IncomeTaxesDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e9212-2031-744b-89bf-650c55fa2e2d" 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_019e9212-2031-781e-91bc-f1df1c88090a" 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_019e9212-2031-744b-89bf-650c55fa2e2d" xlink:to="loc_us-gaap_TaxCreditCarryforwardTable_019e9212-2031-781e-91bc-f1df1c88090a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019e9212-2031-7a3b-a822-652d343fbb7e" 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_019e9212-2031-781e-91bc-f1df1c88090a" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019e9212-2031-7a3b-a822-652d343fbb7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019e9212-2031-7a3b-a822-652d343fbb7e_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_019e9212-2031-7a3b-a822-652d343fbb7e" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019e9212-2031-7a3b-a822-652d343fbb7e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019e9212-2031-788e-b8cd-5a67aa6b9691" 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_019e9212-2031-7a3b-a822-652d343fbb7e" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019e9212-2031-788e-b8cd-5a67aa6b9691" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_019e9212-2031-7dec-b13f-3cbef11d359e" 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_019e9212-2031-788e-b8cd-5a67aa6b9691" xlink:to="loc_us-gaap_DomesticCountryMember_019e9212-2031-7dec-b13f-3cbef11d359e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAxis_019e9212-2031-76c7-b60a-e54118dd15bd" 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_019e9212-2031-781e-91bc-f1df1c88090a" xlink:to="loc_us-gaap_TaxCreditCarryforwardAxis_019e9212-2031-76c7-b60a-e54118dd15bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_019e9212-2031-76c7-b60a-e54118dd15bd_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_019e9212-2031-76c7-b60a-e54118dd15bd" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_019e9212-2031-76c7-b60a-e54118dd15bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_019e9212-2031-702c-9502-cb84463eb2b4" 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_019e9212-2031-76c7-b60a-e54118dd15bd" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_019e9212-2031-702c-9502-cb84463eb2b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CARESActERCProgramMember_019e9212-2031-700a-a07c-5bc4c5902c47" xlink:href="lmnd-20260630.xsd#lmnd_CARESActERCProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardNameDomain_019e9212-2031-702c-9502-cb84463eb2b4" xlink:to="loc_lmnd_CARESActERCProgramMember_019e9212-2031-700a-a07c-5bc4c5902c47" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019e45f1-86e7-7e66-8aba-4a35c4a2bdb0" 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_019e9212-2031-744b-89bf-650c55fa2e2d" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019e45f1-86e7-7e66-8aba-4a35c4a2bdb0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefits_019e45f1-86e7-78bf-a9e7-ec70340d0fb5" 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_019e9212-2031-744b-89bf-650c55fa2e2d" xlink:to="loc_us-gaap_UnrecognizedTaxBenefits_019e45f1-86e7-78bf-a9e7-ec70340d0fb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_019e45f1-86e7-7960-9480-243f8ab91aac" 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_019e9212-2031-744b-89bf-650c55fa2e2d" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_019e45f1-86e7-7960-9480-243f8ab91aac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationTaxCredits_019e920f-23b8-759e-baa9-50d187f92a1b" 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_019e9212-2031-744b-89bf-650c55fa2e2d" xlink:to="loc_us-gaap_IncomeTaxReconciliationTaxCredits_019e920f-23b8-759e-baa9-50d187f92a1b" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/NetLossperShareAntidilutivePotentialCommonSharesDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-7c54-9f6f-8762d0b8051e" 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_019e45f1-86e7-7514-a068-6e75ceae6333" 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_019e45f1-86e7-7c54-9f6f-8762d0b8051e" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019e45f1-86e7-7514-a068-6e75ceae6333" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e45f1-86e7-765b-a332-706995d50eac" 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_019e45f1-86e7-7514-a068-6e75ceae6333" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e45f1-86e7-765b-a332-706995d50eac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e45f1-86e7-765b-a332-706995d50eac_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_019e45f1-86e7-765b-a332-706995d50eac" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e45f1-86e7-765b-a332-706995d50eac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e45f1-86e7-7e67-ae6f-9d0d2518636e" 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_019e45f1-86e7-765b-a332-706995d50eac" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e45f1-86e7-7e67-ae6f-9d0d2518636e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019e45f1-86e7-72f2-9b30-83a70cbcebf6" 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_019e45f1-86e7-7e67-ae6f-9d0d2518636e" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019e45f1-86e7-72f2-9b30-83a70cbcebf6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_019e45f1-86e7-78f0-911f-59b146c5500c" 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_019e45f1-86e7-7e67-ae6f-9d0d2518636e" xlink:to="loc_us-gaap_RestrictedStockMember_019e45f1-86e7-78f0-911f-59b146c5500c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019e45f1-86e7-77cf-a41e-6fe99ac571b5" 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_019e45f1-86e7-7e67-ae6f-9d0d2518636e" xlink:to="loc_us-gaap_WarrantMember_019e45f1-86e7-77cf-a41e-6fe99ac571b5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e45f1-86e7-78b5-8fb6-da5578dd42cf" 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_019e45f1-86e7-7514-a068-6e75ceae6333" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e45f1-86e7-78b5-8fb6-da5578dd42cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e45f1-86e7-78b5-8fb6-da5578dd42cf_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_019e45f1-86e7-78b5-8fb6-da5578dd42cf" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e45f1-86e7-78b5-8fb6-da5578dd42cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e45f1-86e7-7e57-8f68-78188a737b87" 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_019e45f1-86e7-78b5-8fb6-da5578dd42cf" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e45f1-86e7-7e57-8f68-78188a737b87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_MetromileMember_019e45f1-86e7-7ec9-bd8f-9586679d830b" xlink:href="lmnd-20260630.xsd#lmnd_MetromileMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e45f1-86e7-7e57-8f68-78188a737b87" xlink:to="loc_lmnd_MetromileMember_019e45f1-86e7-7ec9-bd8f-9586679d830b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019e45f1-86e7-7404-8be5-eb1ab438ccbc" 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_019e45f1-86e7-7c54-9f6f-8762d0b8051e" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019e45f1-86e7-7404-8be5-eb1ab438ccbc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShareExchangeRatio_019e45f1-86e7-757d-bce8-7d33a77e8445" xlink:href="lmnd-20260630.xsd#lmnd_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShareExchangeRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019e45f1-86e7-7c54-9f6f-8762d0b8051e" xlink:to="loc_lmnd_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuableShareExchangeRatio_019e45f1-86e7-757d-bce8-7d33a77e8445" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/RelatedPartyTransactionsDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-73a4-a3c8-edf5dd0d3df3" 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_019e45f1-86e7-7fb2-af92-98f456ed1403" 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_019e45f1-86e7-73a4-a3c8-edf5dd0d3df3" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019e45f1-86e7-7fb2-af92-98f456ed1403" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e45f1-86e7-7fd0-bfee-0e5a042990d2" 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_019e45f1-86e7-7fb2-af92-98f456ed1403" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e45f1-86e7-7fd0-bfee-0e5a042990d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e45f1-86e7-7fd0-bfee-0e5a042990d2_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_019e45f1-86e7-7fd0-bfee-0e5a042990d2" xlink:to="loc_us-gaap_RelatedPartyDomain_019e45f1-86e7-7fd0-bfee-0e5a042990d2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e45f1-86e7-799b-af2d-a673e67de553" 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_019e45f1-86e7-7fd0-bfee-0e5a042990d2" xlink:to="loc_us-gaap_RelatedPartyDomain_019e45f1-86e7-799b-af2d-a673e67de553" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019e45f1-86e7-70ac-b1e0-6e03fa1d62c1" 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_019e45f1-86e7-799b-af2d-a673e67de553" xlink:to="loc_us-gaap_RelatedPartyMember_019e45f1-86e7-70ac-b1e0-6e03fa1d62c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019e45f1-86e7-7108-a1d1-7a222484e11a" 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_019e45f1-86e7-7fb2-af92-98f456ed1403" xlink:to="loc_srt_CounterpartyNameAxis_019e45f1-86e7-7108-a1d1-7a222484e11a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e45f1-86e7-7108-a1d1-7a222484e11a_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_019e45f1-86e7-7108-a1d1-7a222484e11a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e45f1-86e7-7108-a1d1-7a222484e11a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e45f1-86e7-7c76-83d5-6a961704d95c" 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_019e45f1-86e7-7108-a1d1-7a222484e11a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e45f1-86e7-7c76-83d5-6a961704d95c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeFoundationMember_019e45f1-86e7-7329-8cea-7a40a0725a50" xlink:href="lmnd-20260630.xsd#lmnd_LemonadeFoundationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019e45f1-86e7-7c76-83d5-6a961704d95c" xlink:to="loc_lmnd_LemonadeFoundationMember_019e45f1-86e7-7329-8cea-7a40a0725a50" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e45f1-86e7-73b4-bf55-01e5d2fcaea0" 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_019e45f1-86e7-7fb2-af92-98f456ed1403" xlink:to="loc_dei_LegalEntityAxis_019e45f1-86e7-73b4-bf55-01e5d2fcaea0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e45f1-86e7-73b4-bf55-01e5d2fcaea0_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_019e45f1-86e7-73b4-bf55-01e5d2fcaea0" xlink:to="loc_dei_EntityDomain_019e45f1-86e7-73b4-bf55-01e5d2fcaea0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e45f1-86e7-7889-a515-242f248298b6" 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_019e45f1-86e7-73b4-bf55-01e5d2fcaea0" xlink:to="loc_dei_EntityDomain_019e45f1-86e7-7889-a515-242f248298b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeFoundationMember_019e45f1-86e7-70e1-9a95-5c1892d6c4c1" xlink:href="lmnd-20260630.xsd#lmnd_LemonadeFoundationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e45f1-86e7-7889-a515-242f248298b6" xlink:to="loc_lmnd_LemonadeFoundationMember_019e45f1-86e7-70e1-9a95-5c1892d6c4c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019e45f1-86e7-77b1-ae15-f90155b5236a" 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_019e45f1-86e7-7fb2-af92-98f456ed1403" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019e45f1-86e7-77b1-ae15-f90155b5236a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-77b1-ae15-f90155b5236a_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_019e45f1-86e7-77b1-ae15-f90155b5236a" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-77b1-ae15-f90155b5236a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-7052-b150-381e888f0d14" 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_019e45f1-86e7-77b1-ae15-f90155b5236a" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-7052-b150-381e888f0d14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_LemonadeInc.Member_019e45f1-86e7-79cf-b99a-9df5b92ba9df" xlink:href="lmnd-20260630.xsd#lmnd_LemonadeInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019e45f1-86e7-7052-b150-381e888f0d14" xlink:to="loc_lmnd_LemonadeInc.Member_019e45f1-86e7-79cf-b99a-9df5b92ba9df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_NumberOfSharedDirectors_019e45f1-86e7-71ae-acec-54cdb53b391d" xlink:href="lmnd-20260630.xsd#lmnd_NumberOfSharedDirectors"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019e45f1-86e7-73a4-a3c8-edf5dd0d3df3" xlink:to="loc_lmnd_NumberOfSharedDirectors_019e45f1-86e7-71ae-acec-54cdb53b391d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution_019e45f1-86e7-7d13-aece-e1aa2affd011" xlink:href="lmnd-20260630.xsd#lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019e45f1-86e7-73a4-a3c8-edf5dd0d3df3" xlink:to="loc_lmnd_StockIssuedDuringPeriodSharesIssuedForCharitableContribution_019e45f1-86e7-7d13-aece-e1aa2affd011" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_StockIssuedDuringPeriodIssuedForCharitableContributionFairValue_019e45f1-86e7-7664-b18e-e18f295610cb" xlink:href="lmnd-20260630.xsd#lmnd_StockIssuedDuringPeriodIssuedForCharitableContributionFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019e45f1-86e7-73a4-a3c8-edf5dd0d3df3" xlink:to="loc_lmnd_StockIssuedDuringPeriodIssuedForCharitableContributionFairValue_019e45f1-86e7-7664-b18e-e18f295610cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalanceShares_019e45f1-86e7-79e5-a3a8-0c3c5345b485" 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_019e45f1-86e7-73a4-a3c8-edf5dd0d3df3" xlink:to="loc_us-gaap_InvestmentOwnedBalanceShares_019e45f1-86e7-79e5-a3a8-0c3c5345b485" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_019e45f1-86e7-7661-8e30-62e72e612cf5" 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_019e45f1-86e7-73a4-a3c8-edf5dd0d3df3" xlink:to="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_019e45f1-86e7-7661-8e30-62e72e612cf5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NontradeReceivables_019e45f1-86e7-77cc-a0ab-0e438f165bb6" 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_019e45f1-86e7-73a4-a3c8-edf5dd0d3df3" xlink:to="loc_us-gaap_NontradeReceivables_019e45f1-86e7-77cc-a0ab-0e438f165bb6" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-7c05-b7cc-00d04bab527c" 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_019e45f1-86e7-7260-8062-22fa7041be5c" 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_019e45f1-86e7-7c05-b7cc-00d04bab527c" xlink:to="loc_us-gaap_LossContingenciesTable_019e45f1-86e7-7260-8062-22fa7041be5c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsByNatureAxis_019e45f1-86e7-7997-86a1-c8bfd8fd874d" 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_019e45f1-86e7-7260-8062-22fa7041be5c" xlink:to="loc_us-gaap_GuaranteeObligationsByNatureAxis_019e45f1-86e7-7997-86a1-c8bfd8fd874d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_019e45f1-86e7-7997-86a1-c8bfd8fd874d_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_019e45f1-86e7-7997-86a1-c8bfd8fd874d" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_019e45f1-86e7-7997-86a1-c8bfd8fd874d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_019e45f1-86e7-7803-89b3-780d1b7ee5b4" 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_019e45f1-86e7-7997-86a1-c8bfd8fd874d" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_019e45f1-86e7-7803-89b3-780d1b7ee5b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyLeaseGuaranteeMember_019e45f1-86e7-7eff-a75f-3cd98d943c82" 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_019e45f1-86e7-7803-89b3-780d1b7ee5b4" xlink:to="loc_us-gaap_PropertyLeaseGuaranteeMember_019e45f1-86e7-7eff-a75f-3cd98d943c82" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemAxis_019e45f1-86e7-7b2b-a899-5669aedb7d32" 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_019e45f1-86e7-7260-8062-22fa7041be5c" xlink:to="loc_us-gaap_UnusualOrInfrequentItemAxis_019e45f1-86e7-7b2b-a899-5669aedb7d32" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-7b2b-a899-5669aedb7d32_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_019e45f1-86e7-7b2b-a899-5669aedb7d32" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-7b2b-a899-5669aedb7d32_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-7c29-811e-3c08fc56cef4" 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_019e45f1-86e7-7b2b-a899-5669aedb7d32" xlink:to="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-7c29-811e-3c08fc56cef4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CaliforniaWildfiresMember_019e45f1-86e7-7566-816a-8574d2ce25a4" xlink:href="lmnd-20260630.xsd#lmnd_CaliforniaWildfiresMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualOrInfrequentItemDomain_019e45f1-86e7-7c29-811e-3c08fc56cef4" xlink:to="loc_lmnd_CaliforniaWildfiresMember_019e45f1-86e7-7566-816a-8574d2ce25a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualAtCarryingValue_019e45f1-86e7-7ffb-9c2e-98730fd2f6dd" 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_019e45f1-86e7-7c05-b7cc-00d04bab527c" xlink:to="loc_us-gaap_LossContingencyAccrualAtCarryingValue_019e45f1-86e7-7ffb-9c2e-98730fd2f6dd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GuaranteeObligationsMaximumExposure_019e45f1-86e7-7196-9149-157ddea21235" 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_019e45f1-86e7-7c05-b7cc-00d04bab527c" xlink:to="loc_us-gaap_GuaranteeObligationsMaximumExposure_019e45f1-86e7-7196-9149-157ddea21235" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AssessmentChargePercentageRecoupmentApproved_019e45f1-86e7-7d2d-860a-8934ad830b2f" xlink:href="lmnd-20260630.xsd#lmnd_AssessmentChargePercentageRecoupmentApproved"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019e45f1-86e7-7c05-b7cc-00d04bab527c" xlink:to="loc_lmnd_AssessmentChargePercentageRecoupmentApproved_019e45f1-86e7-7d2d-860a-8934ad830b2f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AssessmentCharge_019e45f1-86e7-70ca-a6db-5e1b989c312e" xlink:href="lmnd-20260630.xsd#lmnd_AssessmentCharge"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019e45f1-86e7-7c05-b7cc-00d04bab527c" xlink:to="loc_lmnd_AssessmentCharge_019e45f1-86e7-70ca-a6db-5e1b989c312e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AssessmentChargeRecoupmentApprovedTerm_019e45f1-86e7-7642-95bd-7f759ea762df" xlink:href="lmnd-20260630.xsd#lmnd_AssessmentChargeRecoupmentApprovedTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019e45f1-86e7-7c05-b7cc-00d04bab527c" xlink:to="loc_lmnd_AssessmentChargeRecoupmentApprovedTerm_019e45f1-86e7-7642-95bd-7f759ea762df" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/SegmentInformationScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" 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_019e45f1-86e7-7703-a15d-5ed9de1ad024" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e45f1-86e7-7703-a15d-5ed9de1ad024" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e45f1-86e7-7ba9-bd61-0577992a2eb0" 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_019e45f1-86e7-7703-a15d-5ed9de1ad024" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e45f1-86e7-7ba9-bd61-0577992a2eb0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e45f1-86e7-7ba9-bd61-0577992a2eb0_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_019e45f1-86e7-7ba9-bd61-0577992a2eb0" xlink:to="loc_us-gaap_SegmentDomain_019e45f1-86e7-7ba9-bd61-0577992a2eb0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e45f1-86e7-71a2-b458-6f9fe541985b" 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_019e45f1-86e7-7ba9-bd61-0577992a2eb0" xlink:to="loc_us-gaap_SegmentDomain_019e45f1-86e7-71a2-b458-6f9fe541985b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_ReportableSegmentMember_019e45f1-86e7-7163-bfb3-5c0b490cceb5" xlink:href="lmnd-20260630.xsd#lmnd_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e45f1-86e7-71a2-b458-6f9fe541985b" xlink:to="loc_lmnd_ReportableSegmentMember_019e45f1-86e7-7163-bfb3-5c0b490cceb5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019e9222-a5cb-76dc-8178-cbc3221198c6" 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_019e45f1-86e7-7703-a15d-5ed9de1ad024" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019e9222-a5cb-76dc-8178-cbc3221198c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019e9222-a5cb-76dc-8178-cbc3221198c6_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_019e9222-a5cb-76dc-8178-cbc3221198c6" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019e9222-a5cb-76dc-8178-cbc3221198c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019e9222-a5cb-7b57-8c6d-3a8cba13e5c1" 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_019e9222-a5cb-76dc-8178-cbc3221198c6" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019e9222-a5cb-7b57-8c6d-3a8cba13e5c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_019e9222-a5cb-7eba-951c-f69c2360db49" 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_019e9222-a5cb-7b57-8c6d-3a8cba13e5c1" xlink:to="loc_us-gaap_DomesticCountryMember_019e9222-a5cb-7eba-951c-f69c2360db49" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAxis_019e9222-a5cb-7d93-bfe3-6fc379f3ea3b" 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_019e45f1-86e7-7703-a15d-5ed9de1ad024" xlink:to="loc_us-gaap_TaxCreditCarryforwardAxis_019e9222-a5cb-7d93-bfe3-6fc379f3ea3b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_019e9222-a5cb-7d93-bfe3-6fc379f3ea3b_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_019e9222-a5cb-7d93-bfe3-6fc379f3ea3b" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_019e9222-a5cb-7d93-bfe3-6fc379f3ea3b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_019e9222-a5cb-74d7-b5b8-72113ecf264e" 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_019e9222-a5cb-7d93-bfe3-6fc379f3ea3b" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_019e9222-a5cb-74d7-b5b8-72113ecf264e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_CARESActERCProgramMember_019e9222-a5cb-7938-a3e1-b75fc4141973" xlink:href="lmnd-20260630.xsd#lmnd_CARESActERCProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardNameDomain_019e9222-a5cb-74d7-b5b8-72113ecf264e" xlink:to="loc_lmnd_CARESActERCProgramMember_019e9222-a5cb-7938-a3e1-b75fc4141973" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019e45f1-86e7-7e0e-b150-87d913a49c65" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_Revenues_019e45f1-86e7-7e0e-b150-87d913a49c65" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_019e45f1-86e7-716b-91cf-d182c7c2ab47" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1_019e45f1-86e7-716b-91cf-d182c7c2ab47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_OtherInsuranceExpense_019e45f1-86e7-728d-8957-edf2eaf696b4" xlink:href="lmnd-20260630.xsd#lmnd_OtherInsuranceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_lmnd_OtherInsuranceExpense_019e45f1-86e7-728d-8957-edf2eaf696b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_019e45f1-86e7-72e1-8416-04dc5238fc21" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_SellingAndMarketingExpense_019e45f1-86e7-72e1-8416-04dc5238fc21" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdvertisingExpense_019e45f1-86e7-7d32-bc1f-2baab5814209" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_AdvertisingExpense_019e45f1-86e7-7d32-bc1f-2baab5814209" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019e45f1-86e7-7595-8147-ea159282eec8" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019e45f1-86e7-7595-8147-ea159282eec8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_GeneralAndAdministrativeLessInterestDepreciationAndOtherSegmentIncomeExpenses_019e45f1-86e7-702d-8e4b-c960e6c23877" xlink:href="lmnd-20260630.xsd#lmnd_GeneralAndAdministrativeLessInterestDepreciationAndOtherSegmentIncomeExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_lmnd_GeneralAndAdministrativeLessInterestDepreciationAndOtherSegmentIncomeExpenses_019e45f1-86e7-702d-8e4b-c960e6c23877" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019e45f1-86e7-7895-af54-3f3723be5a65" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019e45f1-86e7-7895-af54-3f3723be5a65" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization_019e45f1-86e7-76d8-81ef-903ac009dbf0" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization_019e45f1-86e7-76d8-81ef-903ac009dbf0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019e45f1-86e7-7289-8b7a-0c4e420644ea" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019e45f1-86e7-7289-8b7a-0c4e420644ea" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019e45f1-86e7-72d5-8c85-a6b34da273db" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019e45f1-86e7-72d5-8c85-a6b34da273db" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e45f1-86e7-77f8-a08e-0bbc32d4f57b" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_NetIncomeLoss_019e45f1-86e7-77f8-a08e-0bbc32d4f57b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationTaxCredits_019e9222-a5cb-73b7-a708-88311d4a2a05" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_IncomeTaxReconciliationTaxCredits_019e9222-a5cb-73b7-a708-88311d4a2a05" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherExpenses_019e45f1-86e7-7214-854b-cb3ba08a17cb" 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_019e45f1-86e7-7c35-ab8d-e010fdd5e05a" xlink:to="loc_us-gaap_OtherExpenses_019e45f1-86e7-7214-854b-cb3ba08a17cb" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://lemonade.com/role/SegmentInformationScheduleofGrossWrittenPremiumbyStateDetails" xlink:type="simple" xlink:href="lmnd-20260630.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_019e45f1-86e7-773d-be33-8f7116c1c04b" 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_019e45f1-86e7-7a99-b86b-4ecabfdde698" 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_019e45f1-86e7-773d-be33-8f7116c1c04b" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_019e45f1-86e7-7a99-b86b-4ecabfdde698" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019e45f1-86e7-7efd-833b-942fa78ddd1a" 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_019e45f1-86e7-7a99-b86b-4ecabfdde698" xlink:to="loc_srt_StatementGeographicalAxis_019e45f1-86e7-7efd-833b-942fa78ddd1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e45f1-86e7-7efd-833b-942fa78ddd1a_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_019e45f1-86e7-7efd-833b-942fa78ddd1a" xlink:to="loc_srt_SegmentGeographicalDomain_019e45f1-86e7-7efd-833b-942fa78ddd1a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e45f1-86e7-7eb7-8558-e246cad8978b" 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_019e45f1-86e7-7efd-833b-942fa78ddd1a" xlink:to="loc_srt_SegmentGeographicalDomain_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CA_019e45f1-86e7-75a9-82b5-318c52dc9d15" 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_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_stpr_CA_019e45f1-86e7-75a9-82b5-318c52dc9d15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_TX_019e45f1-86e7-7b51-bf42-49fbaf8fffa3" 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_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_stpr_TX_019e45f1-86e7-7b51-bf42-49fbaf8fffa3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_NY_019e45f1-86e7-7bee-aa89-8b79feff11ca" 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_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_stpr_NY_019e45f1-86e7-7bee-aa89-8b79feff11ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_WA_019e45f1-86e7-7179-8e9b-8ca82988445f" 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_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_stpr_WA_019e45f1-86e7-7179-8e9b-8ca82988445f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_IL_019e45f1-86e7-7bbe-af47-cfa7df1b99bf" 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_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_stpr_IL_019e45f1-86e7-7bbe-af47-cfa7df1b99bf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_NJ_019e45f1-86e7-7306-969a-39946b4d576f" 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_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_stpr_NJ_019e45f1-86e7-7306-969a-39946b4d576f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CO_019e45f1-86e7-766c-bb13-dc575aec0dc3" 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_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_stpr_CO_019e45f1-86e7-766c-bb13-dc575aec0dc3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_FL_019e45f1-86e7-7afe-8c76-f1ad71905295" 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_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_stpr_FL_019e45f1-86e7-7afe-8c76-f1ad71905295" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_AZ_019e45f1-86e7-7441-9208-4dabb4e2fc47" 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_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_stpr_AZ_019e45f1-86e7-7441-9208-4dabb4e2fc47" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_PA_019e45f1-86e7-7d15-848e-b67f95d5674c" 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_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_stpr_PA_019e45f1-86e7-7d15-848e-b67f95d5674c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_AllOtherStatesMember_019e45f1-86e7-74f1-8201-a8ff69ea50f3" xlink:href="lmnd-20260630.xsd#lmnd_AllOtherStatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_lmnd_AllOtherStatesMember_019e45f1-86e7-74f1-8201-a8ff69ea50f3" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019e45f1-86e7-7daf-9ae9-2ff79ea9526e" 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_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_country_US_019e45f1-86e7-7daf-9ae9-2ff79ea9526e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_EuropeAndUnitedKingdomMember_019e45f1-86e7-7571-a771-2572de6cad77" xlink:href="lmnd-20260630.xsd#lmnd_EuropeAndUnitedKingdomMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e45f1-86e7-7eb7-8558-e246cad8978b" xlink:to="loc_lmnd_EuropeAndUnitedKingdomMember_019e45f1-86e7-7571-a771-2572de6cad77" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e45f1-86e7-73a5-8144-8169fd505eb5" 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_019e45f1-86e7-7a99-b86b-4ecabfdde698" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e45f1-86e7-73a5-8144-8169fd505eb5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e45f1-86e7-73a5-8144-8169fd505eb5_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_019e45f1-86e7-73a5-8144-8169fd505eb5" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e45f1-86e7-73a5-8144-8169fd505eb5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e45f1-86e7-7ea6-be41-cf4ea8d3632b" 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_019e45f1-86e7-73a5-8144-8169fd505eb5" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e45f1-86e7-7ea6-be41-cf4ea8d3632b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_PremiumsWrittenGrossBenchmarkMember_019e45f1-86e7-7de7-96a4-95879125e2cc" xlink:href="lmnd-20260630.xsd#lmnd_PremiumsWrittenGrossBenchmarkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e45f1-86e7-7ea6-be41-cf4ea8d3632b" xlink:to="loc_lmnd_PremiumsWrittenGrossBenchmarkMember_019e45f1-86e7-7de7-96a4-95879125e2cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019e45f1-86e7-7a3a-9aed-7288a1a0e683" 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_019e45f1-86e7-7a99-b86b-4ecabfdde698" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019e45f1-86e7-7a3a-9aed-7288a1a0e683" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e45f1-86e7-7a3a-9aed-7288a1a0e683_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_019e45f1-86e7-7a3a-9aed-7288a1a0e683" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e45f1-86e7-7a3a-9aed-7288a1a0e683_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e45f1-86e7-7f5d-8bd9-c7690e5fb0e5" 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_019e45f1-86e7-7a3a-9aed-7288a1a0e683" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e45f1-86e7-7f5d-8bd9-c7690e5fb0e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_019e45f1-86e7-71f3-b922-334ebe709cd5" 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_019e45f1-86e7-7f5d-8bd9-c7690e5fb0e5" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_019e45f1-86e7-71f3-b922-334ebe709cd5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PremiumsWrittenGross_019e45f1-86e7-7ee5-8beb-474e36311e05" 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_019e45f1-86e7-773d-be33-8f7116c1c04b" xlink:to="loc_us-gaap_PremiumsWrittenGross_019e45f1-86e7-7ee5-8beb-474e36311e05" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019e45f1-86e7-7d4e-b597-265a71258f15" 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_019e45f1-86e7-773d-be33-8f7116c1c04b" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019e45f1-86e7-7d4e-b597-265a71258f15" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#TradingArrangmentsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllTradingArrangementsMember" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#ecd_AllTradingArrangementsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_lmnd_OfficerTradingArrangementMember_019e45f1-852a-753f-839b-0147b8192ee6" xlink:href="lmnd-20260630.xsd#lmnd_OfficerTradingArrangementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllTradingArrangementsMember" xlink:to="loc_lmnd_OfficerTradingArrangementMember_019e45f1-852a-753f-839b-0147b8192ee6" 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_MayaProsorMember_019e45f1-852a-75b4-8495-e0fce64c56f9" xlink:href="lmnd-20260630.xsd#lmnd_MayaProsorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_lmnd_MayaProsorMember_019e45f1-852a-75b4-8495-e0fce64c56f9" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
