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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e2391-92ae-77be-b523-4eaf6d7045ba,g:8709d1fc-a80e-459a-932e-22514c8eb79e-->
<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://www.flyfrontier.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="simple" xlink:href="fron-20260630.xsd#CondensedConsolidatedStatementsofOperations"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e2391-9354-73b7-8653-3811d341fc75" 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_019e2391-9354-7dac-8a22-69423f1345e0" 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_019e2391-9354-73b7-8653-3811d341fc75" xlink:to="loc_us-gaap_StatementTable_019e2391-9354-7dac-8a22-69423f1345e0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e2391-9354-7333-bd9b-489c2fea0c7f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e2391-9354-7dac-8a22-69423f1345e0" xlink:to="loc_srt_ProductOrServiceAxis_019e2391-9354-7333-bd9b-489c2fea0c7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e2391-9354-7333-bd9b-489c2fea0c7f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019e2391-9354-7333-bd9b-489c2fea0c7f" xlink:to="loc_srt_ProductsAndServicesDomain_019e2391-9354-7333-bd9b-489c2fea0c7f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e2391-9354-7a71-8e5a-4b3156bc5c1c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019e2391-9354-7333-bd9b-489c2fea0c7f" xlink:to="loc_srt_ProductsAndServicesDomain_019e2391-9354-7a71-8e5a-4b3156bc5c1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PassengerMember_019e2391-9354-7442-b94c-0b2cd4d58ecc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PassengerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e2391-9354-7a71-8e5a-4b3156bc5c1c" xlink:to="loc_us-gaap_PassengerMember_019e2391-9354-7442-b94c-0b2cd4d58ecc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductAndServiceOtherMember_019e2391-9354-78c5-bad9-0e720da4058d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductAndServiceOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e2391-9354-7a71-8e5a-4b3156bc5c1c" xlink:to="loc_us-gaap_ProductAndServiceOtherMember_019e2391-9354-78c5-bad9-0e720da4058d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019e2391-9354-78d9-887e-8c860eca252c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2391-9354-73b7-8653-3811d341fc75" xlink:to="loc_us-gaap_RevenuesAbstract_019e2391-9354-78d9-887e-8c860eca252c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e2391-9354-7481-af0a-81da1777762f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019e2391-9354-78d9-887e-8c860eca252c" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e2391-9354-7481-af0a-81da1777762f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_019e2391-9354-7d77-ab1f-8bbbb8d04b84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2391-9354-73b7-8653-3811d341fc75" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_019e2391-9354-7d77-ab1f-8bbbb8d04b84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FuelCosts_019e2391-9354-7ba5-8905-bc1af447a994" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FuelCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e2391-9354-7d77-ab1f-8bbbb8d04b84" xlink:to="loc_us-gaap_FuelCosts_019e2391-9354-7ba5-8905-bc1af447a994" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LaborAndRelatedExpense_019e2391-9354-785c-823b-0445a00524f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LaborAndRelatedExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e2391-9354-7d77-ab1f-8bbbb8d04b84" xlink:to="loc_us-gaap_LaborAndRelatedExpense_019e2391-9354-785c-823b-0445a00524f2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AircraftRental_019e2391-9354-72e2-813a-8d1471743feb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AircraftRental"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e2391-9354-7d77-ab1f-8bbbb8d04b84" xlink:to="loc_us-gaap_AircraftRental_019e2391-9354-72e2-813a-8d1471743feb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandingFeesAndOtherRentals_019e2391-9354-7375-ab1c-652f9c8b5d78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandingFeesAndOtherRentals"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e2391-9354-7d77-ab1f-8bbbb8d04b84" xlink:to="loc_us-gaap_LandingFeesAndOtherRentals_019e2391-9354-7375-ab1c-652f9c8b5d78" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_019e2391-9354-7ee5-8f10-0f577bfc2e5e" 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_CostsAndExpensesAbstract_019e2391-9354-7d77-ab1f-8bbbb8d04b84" xlink:to="loc_us-gaap_SellingAndMarketingExpense_019e2391-9354-7ee5-8f10-0f577bfc2e5e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AircraftMaintenanceMaterialsAndRepairs_019e2391-9354-71a8-9488-26d4e5fae457" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AircraftMaintenanceMaterialsAndRepairs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e2391-9354-7d77-ab1f-8bbbb8d04b84" xlink:to="loc_us-gaap_AircraftMaintenanceMaterialsAndRepairs_019e2391-9354-71a8-9488-26d4e5fae457" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_019e2391-9354-7a3f-9359-2bd68ac42ab1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e2391-9354-7d77-ab1f-8bbbb8d04b84" xlink:to="loc_us-gaap_DepreciationAndAmortization_019e2391-9354-7a3f-9359-2bd68ac42ab1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherOperatingIncomeExpenseNet_019e2391-9354-7295-bc63-a6929ab8d826" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherOperatingIncomeExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e2391-9354-7d77-ab1f-8bbbb8d04b84" xlink:to="loc_us-gaap_OtherOperatingIncomeExpenseNet_019e2391-9354-7295-bc63-a6929ab8d826" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019e2391-9354-7913-a4f5-f15854f6c6bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e2391-9354-7d77-ab1f-8bbbb8d04b84" xlink:to="loc_us-gaap_CostsAndExpenses_019e2391-9354-7913-a4f5-f15854f6c6bc" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019e2391-9354-7dc7-92bc-936f358125ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2391-9354-73b7-8653-3811d341fc75" xlink:to="loc_us-gaap_OperatingIncomeLoss_019e2391-9354-7dc7-92bc-936f358125ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_019e2391-9354-7f96-9081-1541a9259727" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2391-9354-73b7-8653-3811d341fc75" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_019e2391-9354-7f96-9081-1541a9259727" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019e2391-9354-7db9-b2bf-61e1321c6026" 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_OtherNonoperatingIncomeExpenseAbstract_019e2391-9354-7f96-9081-1541a9259727" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019e2391-9354-7db9-b2bf-61e1321c6026" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestCostsCapitalizedAdjustment_019e2391-9354-7f81-9a7c-ee93e5393919" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestCostsCapitalizedAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_019e2391-9354-7f96-9081-1541a9259727" xlink:to="loc_us-gaap_InterestCostsCapitalizedAdjustment_019e2391-9354-7f81-9a7c-ee93e5393919" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_019e2391-9354-7b21-9dc1-3841c59b01de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_019e2391-9354-7f96-9081-1541a9259727" xlink:to="loc_us-gaap_InvestmentIncomeInterest_019e2391-9354-7b21-9dc1-3841c59b01de" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019e2391-9354-70ae-9176-efa60c600def" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_019e2391-9354-7f96-9081-1541a9259727" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019e2391-9354-70ae-9176-efa60c600def" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e2391-9354-7a3c-90ce-9b8294ced1c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2391-9354-73b7-8653-3811d341fc75" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e2391-9354-7a3c-90ce-9b8294ced1c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019e2391-9354-74ab-84dc-556bbb046168" 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_StatementLineItems_019e2391-9354-73b7-8653-3811d341fc75" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019e2391-9354-74ab-84dc-556bbb046168" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e2391-9354-7e13-bad2-0f9cc6e506db" 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_StatementLineItems_019e2391-9354-73b7-8653-3811d341fc75" xlink:to="loc_us-gaap_NetIncomeLoss_019e2391-9354-7e13-bad2-0f9cc6e506db" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicAbstract_019e2391-9354-7eff-8f03-8adf0561a14d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e2391-9354-73b7-8653-3811d341fc75" xlink:to="loc_us-gaap_EarningsPerShareBasicAbstract_019e2391-9354-7eff-8f03-8adf0561a14d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019e2391-9354-7baa-9cf9-8b156184947f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_019e2391-9354-7eff-8f03-8adf0561a14d" xlink:to="loc_us-gaap_EarningsPerShareBasic_019e2391-9354-7baa-9cf9-8b156184947f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019e2391-9354-7086-8912-d4f91f8b3ba4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_019e2391-9354-7eff-8f03-8adf0561a14d" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019e2391-9354-7086-8912-d4f91f8b3ba4" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="fron-20260630.xsd#CondensedConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e2391-9354-769b-8dfa-d343ee7ede2d" 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_019e2391-9354-75fc-abdd-5d58b08343de" 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_019e2391-9354-769b-8dfa-d343ee7ede2d" xlink:to="loc_us-gaap_StatementTable_019e2391-9354-75fc-abdd-5d58b08343de" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e2391-9354-7350-ba93-a642d9185c99" 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_019e2391-9354-75fc-abdd-5d58b08343de" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e2391-9354-7350-ba93-a642d9185c99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e2391-9354-7350-ba93-a642d9185c99_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_019e2391-9354-7350-ba93-a642d9185c99" xlink:to="loc_us-gaap_EquityComponentDomain_019e2391-9354-7350-ba93-a642d9185c99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e2391-9354-78ba-9aaf-2b8c122d6ab5" 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_019e2391-9354-7350-ba93-a642d9185c99" xlink:to="loc_us-gaap_EquityComponentDomain_019e2391-9354-78ba-9aaf-2b8c122d6ab5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e2391-9354-79d9-919b-fd2fb64579f0" 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_019e2391-9354-78ba-9aaf-2b8c122d6ab5" xlink:to="loc_us-gaap_CommonStockMember_019e2391-9354-79d9-919b-fd2fb64579f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019e2391-9354-75d7-b7bc-02e7c15ab173" 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_019e2391-9354-78ba-9aaf-2b8c122d6ab5" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019e2391-9354-75d7-b7bc-02e7c15ab173" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019e2391-9354-7144-814f-a18ea28a279c" 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_019e2391-9354-78ba-9aaf-2b8c122d6ab5" xlink:to="loc_us-gaap_RetainedEarningsMember_019e2391-9354-7144-814f-a18ea28a279c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e2391-9354-70b6-a3de-d01fef98b2c8" 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_019e2391-9354-78ba-9aaf-2b8c122d6ab5" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e2391-9354-70b6-a3de-d01fef98b2c8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2391-9354-76b2-b64a-7e0ed3ddbf31" 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_019e2391-9354-769b-8dfa-d343ee7ede2d" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2391-9354-76b2-b64a-7e0ed3ddbf31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e2391-9354-7472-a365-689807984387" 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_019e2391-9354-76b2-b64a-7e0ed3ddbf31" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019e2391-9354-7472-a365-689807984387" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e2391-9354-7f18-ab97-7c7b6d5bf465" 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_019e2391-9354-76b2-b64a-7e0ed3ddbf31" xlink:to="loc_us-gaap_StockholdersEquity_019e2391-9354-7f18-ab97-7c7b6d5bf465" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e2391-9354-73a7-ad4c-52d8c132cf7d" 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_019e2391-9354-76b2-b64a-7e0ed3ddbf31" xlink:to="loc_us-gaap_NetIncomeLoss_019e2391-9354-73a7-ad4c-52d8c132cf7d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019e2391-9354-78d0-866e-f4e47a36a988" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2391-9354-76b2-b64a-7e0ed3ddbf31" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019e2391-9354-78d0-866e-f4e47a36a988" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_019e2391-9354-7f57-88aa-00cf7c2f316f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2391-9354-76b2-b64a-7e0ed3ddbf31" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_019e2391-9354-7f57-88aa-00cf7c2f316f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_019e2391-9354-7e43-ab31-0d67b5ba9117" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2391-9354-76b2-b64a-7e0ed3ddbf31" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_019e2391-9354-7e43-ab31-0d67b5ba9117" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1_019eb802-5eda-7129-94b7-9b14e32585d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2391-9354-76b2-b64a-7e0ed3ddbf31" xlink:to="loc_us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1_019eb802-5eda-7129-94b7-9b14e32585d5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019eb802-5eda-7a21-b0ea-561d8280fbbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2391-9354-76b2-b64a-7e0ed3ddbf31" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019eb802-5eda-7a21-b0ea-561d8280fbbf" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019e92eb-9ae3-74f5-96cd-ee0ddb389a90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e2391-9354-76b2-b64a-7e0ed3ddbf31" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019e92eb-9ae3-74f5-96cd-ee0ddb389a90" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e92ec-3168-76ad-9208-ea4289d16d8f" 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_019e2391-9354-76b2-b64a-7e0ed3ddbf31" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e92ec-3168-76ad-9208-ea4289d16d8f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e2391-9354-7b39-9df8-7630e7a879cf" 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_019e2391-9354-70ef-8baf-1fe2014178c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/RevenueRecognitionAdditionalInformationDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#RevenueRecognitionAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/RevenueRecognitionAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019f7d53-2de6-7fc9-a179-8ea31c1778d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e2391-9355-7119-a35e-11b9b2442780" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f7d53-2de6-7fc9-a179-8ea31c1778d7" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e2391-9355-7119-a35e-11b9b2442780" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019f7d53-50dd-7797-a673-e04da3823473" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e2391-9355-7119-a35e-11b9b2442780" xlink:to="loc_srt_ProductOrServiceAxis_019f7d53-50dd-7797-a673-e04da3823473" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019f7d53-50dd-7797-a673-e04da3823473_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019f7d53-50dd-7797-a673-e04da3823473" xlink:to="loc_srt_ProductsAndServicesDomain_019f7d53-50dd-7797-a673-e04da3823473_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019f7d53-50dd-7bcc-a117-7009de211f31" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019f7d53-50dd-7797-a673-e04da3823473" xlink:to="loc_srt_ProductsAndServicesDomain_019f7d53-50dd-7bcc-a117-7009de211f31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_UnearnedMembershipFeesMember_019f7d53-50dd-7c3a-9972-0394e2694149" xlink:href="fron-20260630.xsd#fron_UnearnedMembershipFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019f7d53-50dd-7bcc-a117-7009de211f31" xlink:to="loc_fron_UnearnedMembershipFeesMember_019f7d53-50dd-7c3a-9972-0394e2694149" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_ContractWithCustomerLiabilityAirTraffic_019f7d53-2de6-791c-b5bf-d105d3624a92" xlink:href="fron-20260630.xsd#fron_ContractWithCustomerLiabilityAirTraffic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f7d53-2de6-7fc9-a179-8ea31c1778d7" xlink:to="loc_fron_ContractWithCustomerLiabilityAirTraffic_019f7d53-2de6-791c-b5bf-d105d3624a92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_ContractWithCustomerLiabilityRevenueRecognizedPercentage_019f7d53-2de6-789c-88ff-65d098e3d785" xlink:href="fron-20260630.xsd#fron_ContractWithCustomerLiabilityRevenueRecognizedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f7d53-2de6-7fc9-a179-8ea31c1778d7" xlink:to="loc_fron_ContractWithCustomerLiabilityRevenueRecognizedPercentage_019f7d53-2de6-789c-88ff-65d098e3d785" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_ProceedsFromPrepaidLoyaltyProgram_019f7d53-50dd-74f7-a347-e14ec57381cf" xlink:href="fron-20260630.xsd#fron_ProceedsFromPrepaidLoyaltyProgram"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019f7d53-2de6-7fc9-a179-8ea31c1778d7" xlink:to="loc_fron_ProceedsFromPrepaidLoyaltyProgram_019f7d53-50dd-74f7-a347-e14ec57381cf" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/RevenueRecognitionScheduleofDisaggregatedOperatingRevenuesDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#RevenueRecognitionScheduleofDisaggregatedOperatingRevenuesDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/RevenueRecognitionScheduleofDisaggregatedOperatingRevenuesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e2391-9355-70f0-85bf-8fd43d7a3c01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e2391-9355-737a-8803-cacda97b4768" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e2391-9355-70f0-85bf-8fd43d7a3c01" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e2391-9355-737a-8803-cacda97b4768" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e2391-9355-77be-9373-e008546c4b93" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e2391-9355-737a-8803-cacda97b4768" xlink:to="loc_srt_ProductOrServiceAxis_019e2391-9355-77be-9373-e008546c4b93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e2391-9355-77be-9373-e008546c4b93_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019e2391-9355-77be-9373-e008546c4b93" xlink:to="loc_srt_ProductsAndServicesDomain_019e2391-9355-77be-9373-e008546c4b93_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e2391-9355-72b9-9030-08485c421a0e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019e2391-9355-77be-9373-e008546c4b93" xlink:to="loc_srt_ProductsAndServicesDomain_019e2391-9355-72b9-9030-08485c421a0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PassengerMember_019e2391-9355-769a-8585-2d66d3432f2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PassengerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e2391-9355-72b9-9030-08485c421a0e" xlink:to="loc_us-gaap_PassengerMember_019e2391-9355-769a-8585-2d66d3432f2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AircraftFareMember_019e2391-9355-70b0-886e-ec3681bc99ce" xlink:href="fron-20260630.xsd#fron_AircraftFareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PassengerMember_019e2391-9355-769a-8585-2d66d3432f2c" xlink:to="loc_fron_AircraftFareMember_019e2391-9355-70b0-886e-ec3681bc99ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_NonFarePassengerRevenueMember_019e2391-9355-7c8d-b0fe-0f397ca910c8" xlink:href="fron-20260630.xsd#fron_NonFarePassengerRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PassengerMember_019e2391-9355-769a-8585-2d66d3432f2c" xlink:to="loc_fron_NonFarePassengerRevenueMember_019e2391-9355-7c8d-b0fe-0f397ca910c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_PassengerServiceFeesMember_019e2391-9355-7902-b7e0-011641fc0e12" xlink:href="fron-20260630.xsd#fron_PassengerServiceFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fron_NonFarePassengerRevenueMember_019e2391-9355-7c8d-b0fe-0f397ca910c8" xlink:to="loc_fron_PassengerServiceFeesMember_019e2391-9355-7902-b7e0-011641fc0e12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_PassengerBaggageMember_019e2391-9355-7668-9869-367d63e0dd5e" xlink:href="fron-20260630.xsd#fron_PassengerBaggageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fron_NonFarePassengerRevenueMember_019e2391-9355-7c8d-b0fe-0f397ca910c8" xlink:to="loc_fron_PassengerBaggageMember_019e2391-9355-7668-9869-367d63e0dd5e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_PassengerSeatSelectionMember_019e2391-9355-7b03-9fc5-fba974d18de6" xlink:href="fron-20260630.xsd#fron_PassengerSeatSelectionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fron_NonFarePassengerRevenueMember_019e2391-9355-7c8d-b0fe-0f397ca910c8" xlink:to="loc_fron_PassengerSeatSelectionMember_019e2391-9355-7b03-9fc5-fba974d18de6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_OtherPassengerRevenueMember_019e2391-9355-78f4-a2a8-7b6be5f95f88" xlink:href="fron-20260630.xsd#fron_OtherPassengerRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fron_NonFarePassengerRevenueMember_019e2391-9355-7c8d-b0fe-0f397ca910c8" xlink:to="loc_fron_OtherPassengerRevenueMember_019e2391-9355-78f4-a2a8-7b6be5f95f88" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductAndServiceOtherMember_019e2391-9355-71aa-964b-9d3218790295" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductAndServiceOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e2391-9355-72b9-9030-08485c421a0e" xlink:to="loc_us-gaap_ProductAndServiceOtherMember_019e2391-9355-71aa-964b-9d3218790295" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e2391-9355-7f72-b15d-06203f67c39e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e2391-9355-70f0-85bf-8fd43d7a3c01" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e2391-9355-7f72-b15d-06203f67c39e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/RevenueRecognitionScheduleofOperatingRevenuesbyPrincipalGeographicRegionDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#RevenueRecognitionScheduleofOperatingRevenuesbyPrincipalGeographicRegionDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/RevenueRecognitionScheduleofOperatingRevenuesbyPrincipalGeographicRegionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e2391-9355-7f4c-811a-7e7fab989a9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e2391-9355-7c47-be04-8005b69a77b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e2391-9355-7f4c-811a-7e7fab989a9e" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e2391-9355-7c47-be04-8005b69a77b0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirlineDestinationsAxis_019e2391-9355-7cfd-924e-27f55f7019af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirlineDestinationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e2391-9355-7c47-be04-8005b69a77b0" xlink:to="loc_us-gaap_AirlineDestinationsAxis_019e2391-9355-7cfd-924e-27f55f7019af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirlineDestinationDomain_019e2391-9355-7cfd-924e-27f55f7019af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirlineDestinationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AirlineDestinationsAxis_019e2391-9355-7cfd-924e-27f55f7019af" xlink:to="loc_us-gaap_AirlineDestinationDomain_019e2391-9355-7cfd-924e-27f55f7019af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirlineDestinationDomain_019e2391-9355-739e-b932-37799849b5ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirlineDestinationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AirlineDestinationsAxis_019e2391-9355-7cfd-924e-27f55f7019af" xlink:to="loc_us-gaap_AirlineDestinationDomain_019e2391-9355-739e-b932-37799849b5ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticDestinationMember_019e2391-9355-7300-b3d2-56df20672565" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DomesticDestinationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AirlineDestinationDomain_019e2391-9355-739e-b932-37799849b5ba" xlink:to="loc_us-gaap_DomesticDestinationMember_019e2391-9355-7300-b3d2-56df20672565" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LatinAmericaDestinationMember_019e2391-9355-79e0-b4f3-582cb8c3d25a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LatinAmericaDestinationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AirlineDestinationDomain_019e2391-9355-739e-b932-37799849b5ba" xlink:to="loc_us-gaap_LatinAmericaDestinationMember_019e2391-9355-79e0-b4f3-582cb8c3d25a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e2391-9355-7b2c-9c24-b23f4293ba55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e2391-9355-7f4c-811a-7e7fab989a9e" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e2391-9355-7b2c-9c24-b23f4293ba55" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/DebtScheduleofDebtObligationsDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#DebtScheduleofDebtObligationsDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/DebtScheduleofDebtObligationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" 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_019e2391-9355-7eeb-8702-fdf4d6db08c7" 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_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_DebtInstrumentTable_019e2391-9355-7eeb-8702-fdf4d6db08c7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019e2391-9355-739f-b10d-a5dc22a0ed59" 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_019e2391-9355-7eeb-8702-fdf4d6db08c7" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019e2391-9355-739f-b10d-a5dc22a0ed59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-739f-b10d-a5dc22a0ed59_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_019e2391-9355-739f-b10d-a5dc22a0ed59" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-739f-b10d-a5dc22a0ed59_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-723a-9192-82e3d47a4703" 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_019e2391-9355-739f-b10d-a5dc22a0ed59" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-723a-9192-82e3d47a4703" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019e2391-9355-77fe-b1d8-509421b31aec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-723a-9192-82e3d47a4703" xlink:to="loc_us-gaap_SecuredDebtMember_019e2391-9355-77fe-b1d8-509421b31aec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019e2391-9355-7399-bfc6-9df8d979cfca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-723a-9192-82e3d47a4703" xlink:to="loc_us-gaap_UnsecuredDebtMember_019e2391-9355-7399-bfc6-9df8d979cfca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019e2391-9355-7a76-b83e-eafbfce3f683" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2391-9355-7eeb-8702-fdf4d6db08c7" xlink:to="loc_us-gaap_CreditFacilityAxis_019e2391-9355-7a76-b83e-eafbfce3f683" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e2391-9355-7a76-b83e-eafbfce3f683_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019e2391-9355-7a76-b83e-eafbfce3f683" xlink:to="loc_us-gaap_CreditFacilityDomain_019e2391-9355-7a76-b83e-eafbfce3f683_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e2391-9355-7205-881b-c053eba8c199" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019e2391-9355-7a76-b83e-eafbfce3f683" xlink:to="loc_us-gaap_CreditFacilityDomain_019e2391-9355-7205-881b-c053eba8c199" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019e2391-9355-7808-a16e-918766a2d09a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019e2391-9355-7205-881b-c053eba8c199" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019e2391-9355-7808-a16e-918766a2d09a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e2391-9355-7782-8915-306137691139" 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_019e2391-9355-7eeb-8702-fdf4d6db08c7" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e2391-9355-7782-8915-306137691139" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-7782-8915-306137691139_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_019e2391-9355-7782-8915-306137691139" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-7782-8915-306137691139_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-78e3-a06a-5eacf7f815d1" 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_019e2391-9355-7782-8915-306137691139" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-78e3-a06a-5eacf7f815d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_PreDeliveryCreditFacilityMember_019e2391-9355-7401-aa43-bfc52c0f7a6b" xlink:href="fron-20260630.xsd#fron_PreDeliveryCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-78e3-a06a-5eacf7f815d1" xlink:to="loc_fron_PreDeliveryCreditFacilityMember_019e2391-9355-7401-aa43-bfc52c0f7a6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_ClassA1EnhancedEquipmentTrustCertificatesMember_019e2391-9355-7ea6-910d-648a91a9e401" xlink:href="fron-20260630.xsd#fron_ClassA1EnhancedEquipmentTrustCertificatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-78e3-a06a-5eacf7f815d1" xlink:to="loc_fron_ClassA1EnhancedEquipmentTrustCertificatesMember_019e2391-9355-7ea6-910d-648a91a9e401" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AffinityCardAdvancePurchaseMember_019e2391-9355-7351-95fe-70406c243f70" xlink:href="fron-20260630.xsd#fron_AffinityCardAdvancePurchaseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-78e3-a06a-5eacf7f815d1" xlink:to="loc_fron_AffinityCardAdvancePurchaseMember_019e2391-9355-7351-95fe-70406c243f70" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_PayrollSupportProgramPromissoryNoteMember_019e2391-9355-73e5-9666-17347bb190e8" xlink:href="fron-20260630.xsd#fron_PayrollSupportProgramPromissoryNoteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-78e3-a06a-5eacf7f815d1" xlink:to="loc_fron_PayrollSupportProgramPromissoryNoteMember_019e2391-9355-73e5-9666-17347bb190e8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_PayrollSupportProgramPromissoryNoteOneMember_019e2391-9355-7df7-8a19-eeae14e908d1" xlink:href="fron-20260630.xsd#fron_PayrollSupportProgramPromissoryNoteOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fron_PayrollSupportProgramPromissoryNoteMember_019e2391-9355-73e5-9666-17347bb190e8" xlink:to="loc_fron_PayrollSupportProgramPromissoryNoteOneMember_019e2391-9355-7df7-8a19-eeae14e908d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019e2391-9355-79ae-aca4-2b62af86aea9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e2391-9355-7eeb-8702-fdf4d6db08c7" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019e2391-9355-79ae-aca4-2b62af86aea9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e2391-9355-79ae-aca4-2b62af86aea9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e2391-9355-79ae-aca4-2b62af86aea9" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e2391-9355-79ae-aca4-2b62af86aea9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019e2391-9355-7d0f-b978-f3818d2fb4bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019e2391-9355-79ae-aca4-2b62af86aea9" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019e2391-9355-7d0f-b978-f3818d2fb4bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_USDepartmentOfTreasuryCARESActCreditAgreementWarrantsMember_019e2391-9355-788b-996d-a81361c6a257" xlink:href="fron-20260630.xsd#fron_USDepartmentOfTreasuryCARESActCreditAgreementWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019e2391-9355-7d0f-b978-f3818d2fb4bf" xlink:to="loc_fron_USDepartmentOfTreasuryCARESActCreditAgreementWarrantsMember_019e2391-9355-788b-996d-a81361c6a257" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019e2391-9355-77d1-8497-50013c188b7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019e2391-9355-77d1-8497-50013c188b7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LongTermDebtCurrentMaturitiesGross_019e2391-9355-790d-8856-3a8616d8ea8d" xlink:href="fron-20260630.xsd#fron_LongTermDebtCurrentMaturitiesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_fron_LongTermDebtCurrentMaturitiesGross_019e2391-9355-790d-8856-3a8616d8ea8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019e2391-9355-70ba-ae9c-4b84b59ea9f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019e2391-9355-70ba-ae9c-4b84b59ea9f7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019e2391-9355-7c78-9370-c0f4a038bc1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019e2391-9355-7c78-9370-c0f4a038bc1f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019e2391-9355-760e-aad3-5db67037d703" 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_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019e2391-9355-760e-aad3-5db67037d703" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_019e2391-9355-7f83-ba34-1eeb2bdf5ba0" 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_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_DebtInstrumentTerm_019e2391-9355-7f83-ba34-1eeb2bdf5ba0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e2391-9355-748d-8a7a-d64374a3e00e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019e2391-9355-748d-8a7a-d64374a3e00e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_DebtInstrumentInterestRatePeriod_019e2391-9355-7089-9527-15fcd8d03668" xlink:href="fron-20260630.xsd#fron_DebtInstrumentInterestRatePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_fron_DebtInstrumentInterestRatePeriod_019e2391-9355-7089-9527-15fcd8d03668" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019e2391-9355-7863-9d54-11d159d50d13" 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_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019e2391-9355-7863-9d54-11d159d50d13" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019e2391-9355-7eb7-98a4-335dae5dbe4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_019e2391-9355-7eb7-98a4-335dae5dbe4e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019e2391-9355-7ce2-98a4-fd6ef08c19d8" 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_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019e2391-9355-7ce2-98a4-fd6ef08c19d8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_ClassOfWarrantOrRightNumberOfWarrantsExercised_019e2391-9355-7a78-85cc-15defb52bc08" xlink:href="fron-20260630.xsd#fron_ClassOfWarrantOrRightNumberOfWarrantsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_fron_ClassOfWarrantOrRightNumberOfWarrantsExercised_019e2391-9355-7a78-85cc-15defb52bc08" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e2391-9355-761c-8471-fec1d962e99c" 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_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019e2391-9355-761c-8471-fec1d962e99c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExpenseOrRevenueRecognized_019e2391-9355-7313-81b2-1977e0457b64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExpenseOrRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExpenseOrRevenueRecognized_019e2391-9355-7313-81b2-1977e0457b64" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_ClassOfWarrantOrRightNumberOfWarrantsExpired_019e2391-9355-7ed1-80e5-6684754699cd" xlink:href="fron-20260630.xsd#fron_ClassOfWarrantOrRightNumberOfWarrantsExpired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-75dd-8413-097060039008" xlink:to="loc_fron_ClassOfWarrantOrRightNumberOfWarrantsExpired_019e2391-9355-7ed1-80e5-6684754699cd" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/DebtAdditionalInformationDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#DebtAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/DebtAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-767b-b0fe-7390298a18d5" 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_019e2391-9355-7171-8929-0304a72aadde" 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_019e2391-9355-767b-b0fe-7390298a18d5" xlink:to="loc_us-gaap_DebtInstrumentTable_019e2391-9355-7171-8929-0304a72aadde" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019e2391-9355-734b-826d-862572a4585a" 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_019e2391-9355-7171-8929-0304a72aadde" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019e2391-9355-734b-826d-862572a4585a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-734b-826d-862572a4585a_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_019e2391-9355-734b-826d-862572a4585a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-734b-826d-862572a4585a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-7bd6-abfd-570ebb98d195" 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_019e2391-9355-734b-826d-862572a4585a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-7bd6-abfd-570ebb98d195" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019e2391-9355-73c5-bbe0-18da3f7cf87b" 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_019e2391-9355-7bd6-abfd-570ebb98d195" xlink:to="loc_us-gaap_LineOfCreditMember_019e2391-9355-73c5-bbe0-18da3f7cf87b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaid_019e2391-9355-7664-af2d-93925a77efd6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-767b-b0fe-7390298a18d5" xlink:to="loc_us-gaap_InterestPaid_019e2391-9355-7664-af2d-93925a77efd6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_019e2391-9355-7981-8655-d9f289da20ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e2391-9355-767b-b0fe-7390298a18d5" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_019e2391-9355-7981-8655-d9f289da20ed" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/OperatingLeasesEarlyReturnAgreementDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#OperatingLeasesEarlyReturnAgreementDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/OperatingLeasesEarlyReturnAgreementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f826c-9f74-7236-b3a2-d67d1dec7023" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-7402-b861-09358fa9d817" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f826c-9f74-7236-b3a2-d67d1dec7023" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-7402-b861-09358fa9d817" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermAxis_019f826c-9f74-7680-bbbf-d47270750975" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseContractualTermAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-7402-b861-09358fa9d817" xlink:to="loc_us-gaap_LeaseContractualTermAxis_019f826c-9f74-7680-bbbf-d47270750975" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermDomain_019f826c-9f74-7680-bbbf-d47270750975_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseContractualTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LeaseContractualTermAxis_019f826c-9f74-7680-bbbf-d47270750975" xlink:to="loc_us-gaap_LeaseContractualTermDomain_019f826c-9f74-7680-bbbf-d47270750975_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseContractualTermDomain_019f826c-9f74-76f4-af0a-9040aebb7e71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseContractualTermDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LeaseContractualTermAxis_019f826c-9f74-7680-bbbf-d47270750975" xlink:to="loc_us-gaap_LeaseContractualTermDomain_019f826c-9f74-76f4-af0a-9040aebb7e71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_EarlyReturnAgreementMember_019f826c-9f74-773b-81e2-ef6a0434d6d3" xlink:href="fron-20260630.xsd#fron_EarlyReturnAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseContractualTermDomain_019f826c-9f74-76f4-af0a-9040aebb7e71" xlink:to="loc_fron_EarlyReturnAgreementMember_019f826c-9f74-773b-81e2-ef6a0434d6d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_WriteOffNonRecoverableCapitalizedPrepaidMaintenance_019f826c-9f74-7a8a-bf6d-c8e1aec22e2a" xlink:href="fron-20260630.xsd#fron_WriteOffNonRecoverableCapitalizedPrepaidMaintenance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f826c-9f74-7236-b3a2-d67d1dec7023" xlink:to="loc_fron_WriteOffNonRecoverableCapitalizedPrepaidMaintenance_019f826c-9f74-7a8a-bf6d-c8e1aec22e2a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveAcceleratedDepreciation_019f826c-9f74-7eb5-9940-05d45d1a696a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringReserveAcceleratedDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f826c-9f74-7236-b3a2-d67d1dec7023" xlink:to="loc_us-gaap_RestructuringReserveAcceleratedDepreciation_019f826c-9f74-7eb5-9940-05d45d1a696a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_EarlyReturnAgreementCharges_019f826c-9f74-756e-bee3-f18f1770898b" xlink:href="fron-20260630.xsd#fron_EarlyReturnAgreementCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f826c-9f74-7236-b3a2-d67d1dec7023" xlink:to="loc_fron_EarlyReturnAgreementCharges_019f826c-9f74-756e-bee3-f18f1770898b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_EarlyReturnAgreementOtherCharges_019f826c-9f74-7037-96ba-2d9e46b27d6e" xlink:href="fron-20260630.xsd#fron_EarlyReturnAgreementOtherCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f826c-9f74-7236-b3a2-d67d1dec7023" xlink:to="loc_fron_EarlyReturnAgreementOtherCharges_019f826c-9f74-7037-96ba-2d9e46b27d6e" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/OperatingLeasesAircraftDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#OperatingLeasesAircraftDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/OperatingLeasesAircraftDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f7d63-6d44-7a5d-83eb-fea5bbda9a84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-7822-bcfe-a043e3fd3246" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f7d63-6d44-7a5d-83eb-fea5bbda9a84" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-7822-bcfe-a043e3fd3246" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f7d63-6d44-7db8-ae0a-af511ed6b584" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-7822-bcfe-a043e3fd3246" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f7d63-6d44-7db8-ae0a-af511ed6b584" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f7d63-6d44-7db8-ae0a-af511ed6b584_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f7d63-6d44-7db8-ae0a-af511ed6b584" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f7d63-6d44-7db8-ae0a-af511ed6b584_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f7d63-6d44-7b3b-9339-492f4ab3569e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019f7d63-6d44-7db8-ae0a-af511ed6b584" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f7d63-6d44-7b3b-9339-492f4ab3569e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AircraftMember_019f7d63-6d44-7184-870a-4d3a7a605420" xlink:href="fron-20260630.xsd#fron_AircraftMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f7d63-6d44-7b3b-9339-492f4ab3569e" xlink:to="loc_fron_AircraftMember_019f7d63-6d44-7184-870a-4d3a7a605420" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AircraftEngineMember_019f7d63-6d44-7234-bcdd-74233aec47ac" xlink:href="fron-20260630.xsd#fron_AircraftEngineMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f7d63-6d44-7b3b-9339-492f4ab3569e" xlink:to="loc_fron_AircraftEngineMember_019f7d63-6d44-7234-bcdd-74233aec47ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AircraftAndAircraftEnginesMember_019f7d63-9026-73f0-a5d3-70498df2ca9c" xlink:href="fron-20260630.xsd#fron_AircraftAndAircraftEnginesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019f7d63-6d44-7b3b-9339-492f4ab3569e" xlink:to="loc_fron_AircraftAndAircraftEnginesMember_019f7d63-9026-73f0-a5d3-70498df2ca9c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019f7d63-6d44-7840-8fd7-cb0d073f7971" 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_LesseeLeaseDescriptionTable_019e2391-9355-7822-bcfe-a043e3fd3246" xlink:to="loc_srt_RangeAxis_019f7d63-6d44-7840-8fd7-cb0d073f7971" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019f7d63-6d44-7840-8fd7-cb0d073f7971_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_019f7d63-6d44-7840-8fd7-cb0d073f7971" xlink:to="loc_srt_RangeMember_019f7d63-6d44-7840-8fd7-cb0d073f7971_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019f7d63-6d44-7fd6-ba6b-6a75556ede76" 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_019f7d63-6d44-7840-8fd7-cb0d073f7971" xlink:to="loc_srt_RangeMember_019f7d63-6d44-7fd6-ba6b-6a75556ede76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019f7d63-6d44-70d1-917e-b03560a78eb4" 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_019f7d63-6d44-7fd6-ba6b-6a75556ede76" xlink:to="loc_srt_MinimumMember_019f7d63-6d44-70d1-917e-b03560a78eb4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019f7d63-6d44-7d50-b396-6db1ea34637b" 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_019f7d63-6d44-7fd6-ba6b-6a75556ede76" xlink:to="loc_srt_MaximumMember_019f7d63-6d44-7d50-b396-6db1ea34637b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeAxis_019f7d63-9026-726a-ab1c-237e525523fb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-7822-bcfe-a043e3fd3246" xlink:to="loc_srt_AircraftTypeAxis_019f7d63-9026-726a-ab1c-237e525523fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeMember_019f7d63-9026-726a-ab1c-237e525523fb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_AircraftTypeAxis_019f7d63-9026-726a-ab1c-237e525523fb" xlink:to="loc_srt_AircraftTypeMember_019f7d63-9026-726a-ab1c-237e525523fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeMember_019f7d63-9026-737e-8158-c6b4870db023" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_AircraftTypeAxis_019f7d63-9026-726a-ab1c-237e525523fb" xlink:to="loc_srt_AircraftTypeMember_019f7d63-9026-737e-8158-c6b4870db023" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_A320NeoMember_019f7d63-9026-70ff-8c9e-612dcf4ccbac" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_A320NeoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_AircraftTypeMember_019f7d63-9026-737e-8158-c6b4870db023" xlink:to="loc_srt_A320NeoMember_019f7d63-9026-70ff-8c9e-612dcf4ccbac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_019f7d63-9026-7870-be0b-c6ee8d25b37b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleLeasebackTransactionDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-7822-bcfe-a043e3fd3246" xlink:to="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_019f7d63-9026-7870-be0b-c6ee8d25b37b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleLeasebackTransactionNameDomain_019f7d63-9026-7870-be0b-c6ee8d25b37b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleLeasebackTransactionNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_019f7d63-9026-7870-be0b-c6ee8d25b37b" xlink:to="loc_us-gaap_SaleLeasebackTransactionNameDomain_019f7d63-9026-7870-be0b-c6ee8d25b37b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleLeasebackTransactionNameDomain_019f7d63-9026-70ea-8a34-18efcd322ebe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleLeasebackTransactionNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SaleLeasebackTransactionDescriptionAxis_019f7d63-9026-7870-be0b-c6ee8d25b37b" xlink:to="loc_us-gaap_SaleLeasebackTransactionNameDomain_019f7d63-9026-70ea-8a34-18efcd322ebe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AircraftSaleLeasebackMember_019f7d63-9026-7835-a753-6de7cb68794e" xlink:href="fron-20260630.xsd#fron_AircraftSaleLeasebackMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleLeasebackTransactionNameDomain_019f7d63-9026-70ea-8a34-18efcd322ebe" xlink:to="loc_fron_AircraftSaleLeasebackMember_019f7d63-9026-7835-a753-6de7cb68794e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LesseeOperatingLeasesNumberOfLease_019f7d63-6d44-7b25-9f71-aa57287dc421" xlink:href="fron-20260630.xsd#fron_LesseeOperatingLeasesNumberOfLease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f7d63-6d44-7a5d-83eb-fea5bbda9a84" xlink:to="loc_fron_LesseeOperatingLeasesNumberOfLease_019f7d63-6d44-7b25-9f71-aa57287dc421" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019f7d63-6d44-7e0f-8bfe-c504bedff275" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f7d63-6d44-7a5d-83eb-fea5bbda9a84" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019f7d63-6d44-7e0f-8bfe-c504bedff275" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LesseeOperatingLeasesEarlyReturnAgreementNumberOfLeasesExcluded_019f7d63-6d44-7c44-a735-613a44e5d1cb" xlink:href="fron-20260630.xsd#fron_LesseeOperatingLeasesEarlyReturnAgreementNumberOfLeasesExcluded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f7d63-6d44-7a5d-83eb-fea5bbda9a84" xlink:to="loc_fron_LesseeOperatingLeasesEarlyReturnAgreementNumberOfLeasesExcluded_019f7d63-6d44-7c44-a735-613a44e5d1cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LesseeOperatingLeasesNumberOfLeasesWithLeaseRatesDependentOnUsageBasedMetrics_019f7d63-6d44-7322-ad7c-41b81b051195" xlink:href="fron-20260630.xsd#fron_LesseeOperatingLeasesNumberOfLeasesWithLeaseRatesDependentOnUsageBasedMetrics"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f7d63-6d44-7a5d-83eb-fea5bbda9a84" xlink:to="loc_fron_LesseeOperatingLeasesNumberOfLeasesWithLeaseRatesDependentOnUsageBasedMetrics_019f7d63-6d44-7322-ad7c-41b81b051195" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LesseeNumberOfAircraft_019f7d63-9026-762a-9f64-7eaff144762c" xlink:href="fron-20260630.xsd#fron_LesseeNumberOfAircraft"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f7d63-6d44-7a5d-83eb-fea5bbda9a84" xlink:to="loc_fron_LesseeNumberOfAircraft_019f7d63-9026-762a-9f64-7eaff144762c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LeaseNumberOfSaleLeasebackTransactionsNumberOfEngine_019f7d63-9026-7690-b9e9-4fa98b42d2e2" xlink:href="fron-20260630.xsd#fron_LeaseNumberOfSaleLeasebackTransactionsNumberOfEngine"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f7d63-6d44-7a5d-83eb-fea5bbda9a84" xlink:to="loc_fron_LeaseNumberOfSaleLeasebackTransactionsNumberOfEngine_019f7d63-9026-7690-b9e9-4fa98b42d2e2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleAndLeasebackTransactionGainLossNet_019f7d63-9026-7fd2-a9fe-f2c5a7ef2663" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleAndLeasebackTransactionGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019f7d63-6d44-7a5d-83eb-fea5bbda9a84" xlink:to="loc_us-gaap_SaleAndLeasebackTransactionGainLossNet_019f7d63-9026-7fd2-a9fe-f2c5a7ef2663" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/OperatingLeasesAircraftRentExpenseandMaintenanceObligationsDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#OperatingLeasesAircraftRentExpenseandMaintenanceObligationsDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/OperatingLeasesAircraftRentExpenseandMaintenanceObligationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-7738-af6b-9e4f6138965a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-7b9e-bcf9-d5c36440ec73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-7738-af6b-9e4f6138965a" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-7b9e-bcf9-d5c36440ec73" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7911-b2b5-f7efce2a9769" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-7b9e-bcf9-d5c36440ec73" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7911-b2b5-f7efce2a9769" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7911-b2b5-f7efce2a9769_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7911-b2b5-f7efce2a9769" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7911-b2b5-f7efce2a9769_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7b45-8d79-d3a9b77c0431" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7911-b2b5-f7efce2a9769" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7b45-8d79-d3a9b77c0431" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AircraftMember_019e2391-9355-733f-8927-a4cbcd71c9cc" xlink:href="fron-20260630.xsd#fron_AircraftMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7b45-8d79-d3a9b77c0431" xlink:to="loc_fron_AircraftMember_019e2391-9355-733f-8927-a4cbcd71c9cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AircraftRentExpense_019e2391-9355-7a8a-9c70-d926dbe91347" xlink:href="fron-20260630.xsd#fron_AircraftRentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-7738-af6b-9e4f6138965a" xlink:to="loc_fron_AircraftRentExpense_019e2391-9355-7a8a-9c70-d926dbe91347" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_SupplementalRentExpenseBenefitLeaseReturnObligations_019e2391-9355-7a63-b78d-413c6693b7de" xlink:href="fron-20260630.xsd#fron_SupplementalRentExpenseBenefitLeaseReturnObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-7738-af6b-9e4f6138965a" xlink:to="loc_fron_SupplementalRentExpenseBenefitLeaseReturnObligations_019e2391-9355-7a63-b78d-413c6693b7de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AircraftLeaseReturnsLiability_019e2391-9355-794d-95b2-b8a52661a3c3" xlink:href="fron-20260630.xsd#fron_AircraftLeaseReturnsLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-7738-af6b-9e4f6138965a" xlink:to="loc_fron_AircraftLeaseReturnsLiability_019e2391-9355-794d-95b2-b8a52661a3c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_GainLossOnRenewalOfLease_019e2391-9355-7dc4-9912-5efdc5d548cf" xlink:href="fron-20260630.xsd#fron_GainLossOnRenewalOfLease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-7738-af6b-9e4f6138965a" xlink:to="loc_fron_GainLossOnRenewalOfLease_019e2391-9355-7dc4-9912-5efdc5d548cf" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/OperatingLeasesAirportFacilitiesDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#OperatingLeasesAirportFacilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/OperatingLeasesAirportFacilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-7101-ad3e-1e0a28cfe440" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-760a-b5de-068002086310" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-7101-ad3e-1e0a28cfe440" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-760a-b5de-068002086310" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e2391-9355-7c5c-8b8c-4b776ccffc6d" 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_LesseeLeaseDescriptionTable_019e2391-9355-760a-b5de-068002086310" xlink:to="loc_srt_RangeAxis_019e2391-9355-7c5c-8b8c-4b776ccffc6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e2391-9355-7c5c-8b8c-4b776ccffc6d_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_019e2391-9355-7c5c-8b8c-4b776ccffc6d" xlink:to="loc_srt_RangeMember_019e2391-9355-7c5c-8b8c-4b776ccffc6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e2391-9355-78ea-99d7-25160111c876" 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_019e2391-9355-7c5c-8b8c-4b776ccffc6d" xlink:to="loc_srt_RangeMember_019e2391-9355-78ea-99d7-25160111c876" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e2391-9355-7367-bb8a-c94d6e7cfdc2" 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_019e2391-9355-78ea-99d7-25160111c876" xlink:to="loc_srt_MinimumMember_019e2391-9355-7367-bb8a-c94d6e7cfdc2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e2391-9355-7ff9-99d7-c3619560d146" 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_019e2391-9355-78ea-99d7-25160111c876" xlink:to="loc_srt_MaximumMember_019e2391-9355-7ff9-99d7-c3619560d146" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-767a-a2d3-8547dcb5e262" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-760a-b5de-068002086310" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-767a-a2d3-8547dcb5e262" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-767a-a2d3-8547dcb5e262_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-767a-a2d3-8547dcb5e262" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-767a-a2d3-8547dcb5e262_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-71c4-a6ff-cc8790f5a198" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-767a-a2d3-8547dcb5e262" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-71c4-a6ff-cc8790f5a198" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AirportFacilityMember_019e2391-9355-733a-b066-254cf8da02a3" xlink:href="fron-20260630.xsd#fron_AirportFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-71c4-a6ff-cc8790f5a198" xlink:to="loc_fron_AirportFacilityMember_019e2391-9355-733a-b066-254cf8da02a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_NumberOfAirports_019e2391-9355-7e6f-94bb-1e9fa5a4071d" xlink:href="fron-20260630.xsd#fron_NumberOfAirports"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-7101-ad3e-1e0a28cfe440" xlink:to="loc_fron_NumberOfAirports_019e2391-9355-7e6f-94bb-1e9fa5a4071d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019e2391-9355-7db0-b3a3-efc658e06f9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-7101-ad3e-1e0a28cfe440" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019e2391-9355-7db0-b3a3-efc658e06f9e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/OperatingLeasesOtherPropertyandEquipmentDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#OperatingLeasesOtherPropertyandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/OperatingLeasesOtherPropertyandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-725d-b248-6a7d116b6097" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-706f-9f19-da0ab0613a41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-725d-b248-6a7d116b6097" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-706f-9f19-da0ab0613a41" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e2391-9355-7327-9a3c-37869dde709d" 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_LesseeLeaseDescriptionTable_019e2391-9355-706f-9f19-da0ab0613a41" xlink:to="loc_srt_RangeAxis_019e2391-9355-7327-9a3c-37869dde709d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e2391-9355-7327-9a3c-37869dde709d_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_019e2391-9355-7327-9a3c-37869dde709d" xlink:to="loc_srt_RangeMember_019e2391-9355-7327-9a3c-37869dde709d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e2391-9355-76f8-9d16-7ecdef3510dd" 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_019e2391-9355-7327-9a3c-37869dde709d" xlink:to="loc_srt_RangeMember_019e2391-9355-76f8-9d16-7ecdef3510dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e2391-9355-75b9-8e92-826e5393f438" 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_019e2391-9355-76f8-9d16-7ecdef3510dd" xlink:to="loc_srt_MinimumMember_019e2391-9355-75b9-8e92-826e5393f438" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e2391-9355-74fc-be31-2422cf3f1ef6" 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_019e2391-9355-76f8-9d16-7ecdef3510dd" xlink:to="loc_srt_MaximumMember_019e2391-9355-74fc-be31-2422cf3f1ef6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7773-af44-e31c0b393204" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-706f-9f19-da0ab0613a41" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7773-af44-e31c0b393204" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7773-af44-e31c0b393204_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7773-af44-e31c0b393204" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7773-af44-e31c0b393204_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7828-879a-af09395656db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7773-af44-e31c0b393204" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7828-879a-af09395656db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_OtherGroundPropertyAndEquipmentMember_019e2391-9355-7405-9ff5-d5ca60ac47db" xlink:href="fron-20260630.xsd#fron_OtherGroundPropertyAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7828-879a-af09395656db" xlink:to="loc_fron_OtherGroundPropertyAndEquipmentMember_019e2391-9355-7405-9ff5-d5ca60ac47db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019e2391-9355-7ea9-918e-d016c113a56d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-725d-b248-6a7d116b6097" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_019e2391-9355-7ea9-918e-d016c113a56d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/OperatingLeasesAdditionalInformationDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#OperatingLeasesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/OperatingLeasesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-75fe-b0d6-148e95a7210b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-764d-af49-05ec011c76aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-75fe-b0d6-148e95a7210b" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-764d-af49-05ec011c76aa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7f7d-8ce4-ff80fb8d5040" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019e2391-9355-764d-af49-05ec011c76aa" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7f7d-8ce4-ff80fb8d5040" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7f7d-8ce4-ff80fb8d5040_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7f7d-8ce4-ff80fb8d5040" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7f7d-8ce4-ff80fb8d5040_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7d2c-922c-71eba6e01619" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7f7d-8ce4-ff80fb8d5040" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7d2c-922c-71eba6e01619" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AircraftAndAircraftEnginesMember_019e2391-9355-730d-a105-4c45b59120f2" xlink:href="fron-20260630.xsd#fron_AircraftAndAircraftEnginesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7d2c-922c-71eba6e01619" xlink:to="loc_fron_AircraftAndAircraftEnginesMember_019e2391-9355-730d-a105-4c45b59120f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_019e2391-9355-7d84-b531-bbd9defbb5f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-75fe-b0d6-148e95a7210b" xlink:to="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_019e2391-9355-7d84-b531-bbd9defbb5f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_019f8aaf-8267-75da-9c68-e785c8b438e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-75fe-b0d6-148e95a7210b" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_019f8aaf-8267-75da-9c68-e785c8b438e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_019f7d66-55ea-7992-9378-8bf504980cdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-75fe-b0d6-148e95a7210b" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_019f7d66-55ea-7992-9378-8bf504980cdf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasePayments_019e2391-9355-7e08-b662-31fffdb7b655" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeasePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019e2391-9355-75fe-b0d6-148e95a7210b" xlink:to="loc_us-gaap_OperatingLeasePayments_019e2391-9355-7e08-b662-31fffdb7b655" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/StockBasedCompensationStockOptionsRestrictedStockUnitsandPerformanceStockUnitsDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#StockBasedCompensationStockOptionsRestrictedStockUnitsandPerformanceStockUnitsDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/StockBasedCompensationStockOptionsRestrictedStockUnitsandPerformanceStockUnitsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-932d-77c6-92f9-89fea1fe4f2e" 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_019e2391-9355-7b36-b5a9-43f8aff54ccc" 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_019f1812-932d-77c6-92f9-89fea1fe4f2e" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e2391-9355-7b36-b5a9-43f8aff54ccc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019f1812-932d-75ef-accf-32a48d87042c" 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_019e2391-9355-7b36-b5a9-43f8aff54ccc" xlink:to="loc_us-gaap_AwardTypeAxis_019f1812-932d-75ef-accf-32a48d87042c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019f1812-932d-75ef-accf-32a48d87042c_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_019f1812-932d-75ef-accf-32a48d87042c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019f1812-932d-75ef-accf-32a48d87042c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019f1812-932d-7141-a2fe-56e7c5fb649c" 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_019f1812-932d-75ef-accf-32a48d87042c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019f1812-932d-7141-a2fe-56e7c5fb649c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019f1812-932d-73ab-b678-0d6a8f4092ab" 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_019f1812-932d-7141-a2fe-56e7c5fb649c" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019f1812-932d-73ab-b678-0d6a8f4092ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019f1812-abae-73c0-83f9-18cd51038e7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019f1812-932d-7141-a2fe-56e7c5fb649c" xlink:to="loc_us-gaap_PerformanceSharesMember_019f1812-abae-73c0-83f9-18cd51038e7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019f1812-abae-79a5-9f8c-4499f19bf781" 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_019e2391-9355-7b36-b5a9-43f8aff54ccc" xlink:to="loc_us-gaap_PlanNameAxis_019f1812-abae-79a5-9f8c-4499f19bf781" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019f1812-abae-79a5-9f8c-4499f19bf781_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_019f1812-abae-79a5-9f8c-4499f19bf781" xlink:to="loc_us-gaap_PlanNameDomain_019f1812-abae-79a5-9f8c-4499f19bf781_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019f1812-abae-72fb-ba6c-0481fe2a3494" 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_019f1812-abae-79a5-9f8c-4499f19bf781" xlink:to="loc_us-gaap_PlanNameDomain_019f1812-abae-72fb-ba6c-0481fe2a3494" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_A2021LTIPlanMember_019f1812-abae-73e1-a8ea-f356c2c33b7a" xlink:href="fron-20260630.xsd#fron_A2021LTIPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019f1812-abae-72fb-ba6c-0481fe2a3494" xlink:to="loc_fron_A2021LTIPlanMember_019f1812-abae-73e1-a8ea-f356c2c33b7a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_019f1812-abae-7943-961f-2b10a42eac2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e2391-9355-7b36-b5a9-43f8aff54ccc" xlink:to="loc_us-gaap_VestingAxis_019f1812-abae-7943-961f-2b10a42eac2a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019f1812-abae-7943-961f-2b10a42eac2a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_019f1812-abae-7943-961f-2b10a42eac2a" xlink:to="loc_us-gaap_VestingDomain_019f1812-abae-7943-961f-2b10a42eac2a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019f1812-abae-7150-867c-b91b90f3da66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_019f1812-abae-7943-961f-2b10a42eac2a" xlink:to="loc_us-gaap_VestingDomain_019f1812-abae-7150-867c-b91b90f3da66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_NonMarketBasedConditionMember_019f1812-abae-7c00-b7fe-97ddd7357f55" xlink:href="fron-20260630.xsd#fron_NonMarketBasedConditionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019f1812-abae-7150-867c-b91b90f3da66" xlink:to="loc_fron_NonMarketBasedConditionMember_019f1812-abae-7c00-b7fe-97ddd7357f55" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_MarketBasedConditionMember_019f1812-abae-702d-bcca-20b9a0e92455" xlink:href="fron-20260630.xsd#fron_MarketBasedConditionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019f1812-abae-7150-867c-b91b90f3da66" xlink:to="loc_fron_MarketBasedConditionMember_019f1812-abae-702d-bcca-20b9a0e92455" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019f1812-932d-78c9-92b6-61bfed73101b" 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_019f1812-932d-77c6-92f9-89fea1fe4f2e" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019f1812-932d-78c9-92b6-61bfed73101b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019f1812-932d-72a4-9f54-cd23ddf540f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-932d-77c6-92f9-89fea1fe4f2e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019f1812-932d-72a4-9f54-cd23ddf540f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019f1812-932d-7aed-bce8-973ce6aacefc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-932d-77c6-92f9-89fea1fe4f2e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019f1812-932d-7aed-bce8-973ce6aacefc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019f1812-932d-7d3a-9c63-8eefb1e49370" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-932d-77c6-92f9-89fea1fe4f2e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019f1812-932d-7d3a-9c63-8eefb1e49370" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019f1812-932d-7281-8584-30fd558bd058" 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_019f1812-932d-77c6-92f9-89fea1fe4f2e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019f1812-932d-7281-8584-30fd558bd058" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019f1812-932d-7df5-a101-9b8ab2437517" 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_019f1812-932d-77c6-92f9-89fea1fe4f2e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019f1812-932d-7df5-a101-9b8ab2437517" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019f1812-932d-7ad4-922b-004204d674f2" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-932d-77c6-92f9-89fea1fe4f2e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019f1812-932d-7ad4-922b-004204d674f2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_019f1812-932d-7334-b1a6-1c159ffabb80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-932d-77c6-92f9-89fea1fe4f2e" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_019f1812-932d-7334-b1a6-1c159ffabb80" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019f1812-932d-78f6-8e6e-70490d753e78" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-932d-77c6-92f9-89fea1fe4f2e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019f1812-932d-78f6-8e6e-70490d753e78" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_ShareBasedPaymentArrangementSharesWithheldForTaxWithholdingObligationWeightedAverageGrantDateFairValue_019f1812-932d-716d-bb0b-a07502385eb6" xlink:href="fron-20260630.xsd#fron_ShareBasedPaymentArrangementSharesWithheldForTaxWithholdingObligationWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-932d-77c6-92f9-89fea1fe4f2e" xlink:to="loc_fron_ShareBasedPaymentArrangementSharesWithheldForTaxWithholdingObligationWeightedAverageGrantDateFairValue_019f1812-932d-716d-bb0b-a07502385eb6" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/StockBasedCompensationStockholdersEquityDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#StockBasedCompensationStockholdersEquityDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/StockBasedCompensationStockholdersEquityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-74f8-7e9a-b554-c1b3c6f24608" 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_019e2391-9355-7c9e-a5e0-8a5911f2ec2e" 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_019f1812-74f8-7e9a-b554-c1b3c6f24608" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e2391-9355-7c9e-a5e0-8a5911f2ec2e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019f1812-74f8-76d6-a1a1-5864febc03b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e2391-9355-7c9e-a5e0-8a5911f2ec2e" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019f1812-74f8-76d6-a1a1-5864febc03b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f1812-74f8-76d6-a1a1-5864febc03b8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f1812-74f8-76d6-a1a1-5864febc03b8" xlink:to="loc_us-gaap_ClassOfStockDomain_019f1812-74f8-76d6-a1a1-5864febc03b8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f1812-74f8-7d9c-a667-26e7c236ff85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f1812-74f8-76d6-a1a1-5864febc03b8" xlink:to="loc_us-gaap_ClassOfStockDomain_019f1812-74f8-7d9c-a667-26e7c236ff85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonvotingCommonStockMember_019f1812-74f8-7344-b9f6-2a7286259184" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonvotingCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f1812-74f8-7d9c-a667-26e7c236ff85" xlink:to="loc_us-gaap_NonvotingCommonStockMember_019f1812-74f8-7344-b9f6-2a7286259184" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019f1812-74f8-7f17-b9ee-fc182beac112" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-74f8-7e9a-b554-c1b3c6f24608" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019f1812-74f8-7f17-b9ee-fc182beac112" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019f1812-74f8-7689-8b4a-97a3bb33814b" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-74f8-7e9a-b554-c1b3c6f24608" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019f1812-74f8-7689-8b4a-97a3bb33814b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019f1812-74f8-718c-8255-72168859a7df" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-74f8-7e9a-b554-c1b3c6f24608" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019f1812-74f8-718c-8255-72168859a7df" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019f1812-74f8-789e-b21b-20662243fb5f" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019f1812-74f8-7e9a-b554-c1b3c6f24608" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019f1812-74f8-789e-b21b-20662243fb5f" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/CommitmentsandContingenciesScheduleofAircraftandEngineOrdersDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#CommitmentsandContingenciesScheduleofAircraftandEngineOrdersDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/CommitmentsandContingenciesScheduleofAircraftandEngineOrdersDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-702a-ad8a-a9691aba980b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermPurchaseCommitmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7eda-96a3-f41aeba3a20f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermPurchaseCommitmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-702a-ad8a-a9691aba980b" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7eda-96a3-f41aeba3a20f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeAxis_019e2391-9355-7057-83a9-e244a09ac54e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7eda-96a3-f41aeba3a20f" xlink:to="loc_srt_AircraftTypeAxis_019e2391-9355-7057-83a9-e244a09ac54e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeMember_019e2391-9355-7057-83a9-e244a09ac54e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_AircraftTypeAxis_019e2391-9355-7057-83a9-e244a09ac54e" xlink:to="loc_srt_AircraftTypeMember_019e2391-9355-7057-83a9-e244a09ac54e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AircraftTypeMember_019e2391-9355-7d51-8bcb-5680f38896c4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AircraftTypeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_AircraftTypeAxis_019e2391-9355-7057-83a9-e244a09ac54e" xlink:to="loc_srt_AircraftTypeMember_019e2391-9355-7d51-8bcb-5680f38896c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_A320NeoMember_019e2391-9355-7621-8224-fac48734e59d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_A320NeoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_AircraftTypeMember_019e2391-9355-7d51-8bcb-5680f38896c4" xlink:to="loc_srt_A320NeoMember_019e2391-9355-7621-8224-fac48734e59d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_A321NeoMember_019e2391-9355-7045-8f87-cbae2615b67b" xlink:href="fron-20260630.xsd#fron_A321NeoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_AircraftTypeMember_019e2391-9355-7d51-8bcb-5680f38896c4" xlink:to="loc_fron_A321NeoMember_019e2391-9355-7045-8f87-cbae2615b67b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7959-8d5b-59d421a5ff9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7eda-96a3-f41aeba3a20f" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7959-8d5b-59d421a5ff9e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7959-8d5b-59d421a5ff9e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7959-8d5b-59d421a5ff9e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-7959-8d5b-59d421a5ff9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-73ca-bcba-7795f945c12f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e2391-9355-7959-8d5b-59d421a5ff9e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-73ca-bcba-7795f945c12f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirTransportationEquipmentMember_019e2391-9355-7631-8dde-73834c7d258b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AirTransportationEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-73ca-bcba-7795f945c12f" xlink:to="loc_us-gaap_AirTransportationEquipmentMember_019e2391-9355-7631-8dde-73834c7d258b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AircraftEngineMember_019e2391-9355-7798-a67b-64b1fd2fdc2e" xlink:href="fron-20260630.xsd#fron_AircraftEngineMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e2391-9355-73ca-bcba-7795f945c12f" xlink:to="loc_fron_AircraftEngineMember_019e2391-9355-7798-a67b-64b1fd2fdc2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredRemainderOfFiscalYear_019e2391-9355-79fb-ae0e-0ec0db434234" xlink:href="fron-20260630.xsd#fron_LongTermPurchaseCommitmentMinimumQuantityRequiredRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-702a-ad8a-a9691aba980b" xlink:to="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredRemainderOfFiscalYear_019e2391-9355-79fb-ae0e-0ec0db434234" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearOne_019e2391-9355-7794-80ce-59136a32d5b7" xlink:href="fron-20260630.xsd#fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearOne"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-702a-ad8a-a9691aba980b" xlink:to="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearOne_019e2391-9355-7794-80ce-59136a32d5b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearTwo_019e2391-9355-7450-afc3-fdb0b44fc3e3" xlink:href="fron-20260630.xsd#fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-702a-ad8a-a9691aba980b" xlink:to="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearTwo_019e2391-9355-7450-afc3-fdb0b44fc3e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearThree_019e2391-9355-74dd-9670-39ea04f2b801" xlink:href="fron-20260630.xsd#fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-702a-ad8a-a9691aba980b" xlink:to="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearThree_019e2391-9355-74dd-9670-39ea04f2b801" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearFour_019e2391-9355-7e17-8e6b-07b1d8d4ae80" xlink:href="fron-20260630.xsd#fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-702a-ad8a-a9691aba980b" xlink:to="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredYearFour_019e2391-9355-7e17-8e6b-07b1d8d4ae80" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredAfterYearFour_019e2391-9355-7f29-b584-413f782c335d" xlink:href="fron-20260630.xsd#fron_LongTermPurchaseCommitmentMinimumQuantityRequiredAfterYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-702a-ad8a-a9691aba980b" xlink:to="loc_fron_LongTermPurchaseCommitmentMinimumQuantityRequiredAfterYearFour_019e2391-9355-7f29-b584-413f782c335d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentMinimumQuantityRequired_019e2391-9355-71b1-addb-c3ff3664aea8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermPurchaseCommitmentMinimumQuantityRequired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-702a-ad8a-a9691aba980b" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentMinimumQuantityRequired_019e2391-9355-71b1-addb-c3ff3664aea8" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/CommitmentsandContingenciesAdditionalInformationDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#CommitmentsandContingenciesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/CommitmentsandContingenciesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermPurchaseCommitmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7cd2-a98c-43529cd0137e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermPurchaseCommitmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7cd2-a98c-43529cd0137e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019e2391-9355-7505-bcf3-dd9bbb4a1d07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7cd2-a98c-43529cd0137e" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019e2391-9355-7505-bcf3-dd9bbb4a1d07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameAxis_019e2391-9355-7ad7-86c4-5a6d8415f8c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7cd2-a98c-43529cd0137e" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameAxis_019e2391-9355-7ad7-86c4-5a6d8415f8c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameDomain_019e2391-9355-7ad7-86c4-5a6d8415f8c3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameAxis_019e2391-9355-7ad7-86c4-5a6d8415f8c3" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameDomain_019e2391-9355-7ad7-86c4-5a6d8415f8c3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameDomain_019e2391-9355-7f05-9da1-c47ee9839f38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameAxis_019e2391-9355-7ad7-86c4-5a6d8415f8c3" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameDomain_019e2391-9355-7f05-9da1-c47ee9839f38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalRevenueServiceIRSMember_019e2391-9355-71e8-b10e-4597f2907a42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternalRevenueServiceIRSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameDomain_019e2391-9355-7f05-9da1-c47ee9839f38" xlink:to="loc_us-gaap_InternalRevenueServiceIRSMember_019e2391-9355-71e8-b10e-4597f2907a42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseAxis_019e2391-9355-7a9c-b5e5-75e6449d8f68" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7cd2-a98c-43529cd0137e" xlink:to="loc_srt_LitigationCaseAxis_019e2391-9355-7a9c-b5e5-75e6449d8f68" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019e2391-9355-7a9c-b5e5-75e6449d8f68_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_LitigationCaseAxis_019e2391-9355-7a9c-b5e5-75e6449d8f68" xlink:to="loc_srt_LitigationCaseTypeDomain_019e2391-9355-7a9c-b5e5-75e6449d8f68_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019e2391-9355-7d4f-bad0-28d52983a70e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_LitigationCaseAxis_019e2391-9355-7a9c-b5e5-75e6449d8f68" xlink:to="loc_srt_LitigationCaseTypeDomain_019e2391-9355-7d4f-bad0-28d52983a70e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_U.S.TransportationSecurityAdministrationMember_019e2391-9355-75c4-99e0-561bab71a2bd" xlink:href="fron-20260630.xsd#fron_U.S.TransportationSecurityAdministrationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_019e2391-9355-7d4f-bad0-28d52983a70e" xlink:to="loc_fron_U.S.TransportationSecurityAdministrationMember_019e2391-9355-75c4-99e0-561bab71a2bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreproductionCostsRelatedToLongTermSupplyArrangementsCostsCapitalized_019e2391-9355-7863-a6a3-5dbc96c8b430" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreproductionCostsRelatedToLongTermSupplyArrangementsCostsCapitalized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_PreproductionCostsRelatedToLongTermSupplyArrangementsCostsCapitalized_019e2391-9355-7863-a6a3-5dbc96c8b430" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationEstimateOfPossibleLoss_019e2391-9355-7b2b-b345-2a405c642418" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExaminationEstimateOfPossibleLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_IncomeTaxExaminationEstimateOfPossibleLoss_019e2391-9355-7b2b-b345-2a405c642418" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementExpense_019e2391-9355-7fb8-b46b-352d849b9a96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_LitigationSettlementExpense_019e2391-9355-7fb8-b46b-352d849b9a96" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationReserve_019e2391-9355-78a5-9d84-a7d5963acec7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_LitigationReserve_019e2391-9355-78a5-9d84-a7d5963acec7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_MultiemployerPlanNumberOfEmployeeGroups_019e2391-9355-78d2-bb74-1479ed4a7a6e" xlink:href="fron-20260630.xsd#fron_MultiemployerPlanNumberOfEmployeeGroups"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_fron_MultiemployerPlanNumberOfEmployeeGroups_019e2391-9355-78d2-bb74-1479ed4a7a6e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementToAllEntitysEmployeesPercentage_019e2391-9355-7102-865b-8a42a9bed5d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementToAllEntitysEmployeesPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementToAllEntitysEmployeesPercentage_019e2391-9355-7102-865b-8a42a9bed5d6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SelfInsuranceReserve_019e2391-9355-7b04-9e03-5bdcaa9f4f69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SelfInsuranceReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_SelfInsuranceReserve_019e2391-9355-7b04-9e03-5bdcaa9f4f69" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/CommitmentsandContingenciesAdditionalInformationDetails_1" xlink:type="simple" xlink:href="fron-20260630.xsd#CommitmentsandContingenciesAdditionalInformationDetails_1"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/CommitmentsandContingenciesAdditionalInformationDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermPurchaseCommitmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7cd2-a98c-43529cd0137e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermPurchaseCommitmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7cd2-a98c-43529cd0137e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameAxis_019e2391-9355-7ad7-86c4-5a6d8415f8c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7cd2-a98c-43529cd0137e" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameAxis_019e2391-9355-7ad7-86c4-5a6d8415f8c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameDomain_019e2391-9355-7ad7-86c4-5a6d8415f8c3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameAxis_019e2391-9355-7ad7-86c4-5a6d8415f8c3" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameDomain_019e2391-9355-7ad7-86c4-5a6d8415f8c3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityNameDomain_019e2391-9355-7f05-9da1-c47ee9839f38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameAxis_019e2391-9355-7ad7-86c4-5a6d8415f8c3" xlink:to="loc_us-gaap_IncomeTaxAuthorityNameDomain_019e2391-9355-7f05-9da1-c47ee9839f38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalRevenueServiceIRSMember_019e2391-9355-71e8-b10e-4597f2907a42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternalRevenueServiceIRSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityNameDomain_019e2391-9355-7f05-9da1-c47ee9839f38" xlink:to="loc_us-gaap_InternalRevenueServiceIRSMember_019e2391-9355-71e8-b10e-4597f2907a42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseAxis_019e2391-9355-7a9c-b5e5-75e6449d8f68" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_019e2391-9355-7cd2-a98c-43529cd0137e" xlink:to="loc_srt_LitigationCaseAxis_019e2391-9355-7a9c-b5e5-75e6449d8f68" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019e2391-9355-7a9c-b5e5-75e6449d8f68_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_LitigationCaseAxis_019e2391-9355-7a9c-b5e5-75e6449d8f68" xlink:to="loc_srt_LitigationCaseTypeDomain_019e2391-9355-7a9c-b5e5-75e6449d8f68_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019e2391-9355-7d4f-bad0-28d52983a70e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_LitigationCaseAxis_019e2391-9355-7a9c-b5e5-75e6449d8f68" xlink:to="loc_srt_LitigationCaseTypeDomain_019e2391-9355-7d4f-bad0-28d52983a70e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_U.S.TransportationSecurityAdministrationMember_019e2391-9355-75c4-99e0-561bab71a2bd" xlink:href="fron-20260630.xsd#fron_U.S.TransportationSecurityAdministrationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_019e2391-9355-7d4f-bad0-28d52983a70e" xlink:to="loc_fron_U.S.TransportationSecurityAdministrationMember_019e2391-9355-75c4-99e0-561bab71a2bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreproductionCostsRelatedToLongTermSupplyArrangementsCostsCapitalized_019e2391-9355-7863-a6a3-5dbc96c8b430" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreproductionCostsRelatedToLongTermSupplyArrangementsCostsCapitalized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_PreproductionCostsRelatedToLongTermSupplyArrangementsCostsCapitalized_019e2391-9355-7863-a6a3-5dbc96c8b430" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationEstimateOfPossibleLoss_019e2391-9355-7b2b-b345-2a405c642418" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExaminationEstimateOfPossibleLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_IncomeTaxExaminationEstimateOfPossibleLoss_019e2391-9355-7b2b-b345-2a405c642418" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementExpense_019e2391-9355-7fb8-b46b-352d849b9a96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_LitigationSettlementExpense_019e2391-9355-7fb8-b46b-352d849b9a96" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationReserve_019e2391-9355-78a5-9d84-a7d5963acec7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_LitigationReserve_019e2391-9355-78a5-9d84-a7d5963acec7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_MultiemployerPlanNumberOfEmployeeGroups_019e2391-9355-78d2-bb74-1479ed4a7a6e" xlink:href="fron-20260630.xsd#fron_MultiemployerPlanNumberOfEmployeeGroups"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_fron_MultiemployerPlanNumberOfEmployeeGroups_019e2391-9355-78d2-bb74-1479ed4a7a6e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementToAllEntitysEmployeesPercentage_019e2391-9355-7102-865b-8a42a9bed5d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementToAllEntitysEmployeesPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementToAllEntitysEmployeesPercentage_019e2391-9355-7102-865b-8a42a9bed5d6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SelfInsuranceReserve_019e2391-9355-7b04-9e03-5bdcaa9f4f69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SelfInsuranceReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_019e2391-9355-73d2-bad4-7a7d4b5c6c3f" xlink:to="loc_us-gaap_SelfInsuranceReserve_019e2391-9355-7b04-9e03-5bdcaa9f4f69" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/CommitmentsandContingenciesScheduleofCollectiveBargainingAgreementsDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#CommitmentsandContingenciesScheduleofCollectiveBargainingAgreementsDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/CommitmentsandContingenciesScheduleofCollectiveBargainingAgreementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MultiemployerPlansLineItems_019e2391-9355-741d-9dcf-c605b7f25e44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MultiemployerPlansLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfMultiemployerPlansTable_019e2391-9355-7618-bdb7-2196ac096d80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfMultiemployerPlansTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MultiemployerPlansLineItems_019e2391-9355-741d-9dcf-c605b7f25e44" xlink:to="loc_us-gaap_ScheduleOfMultiemployerPlansTable_019e2391-9355-7618-bdb7-2196ac096d80" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollectiveBargainingArrangementAxis_019e2391-9355-7cbb-8527-edcc56fa091f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollectiveBargainingArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfMultiemployerPlansTable_019e2391-9355-7618-bdb7-2196ac096d80" xlink:to="loc_us-gaap_CollectiveBargainingArrangementAxis_019e2391-9355-7cbb-8527-edcc56fa091f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollectiveBargainingArrangementDomain_019e2391-9355-7cbb-8527-edcc56fa091f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollectiveBargainingArrangementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CollectiveBargainingArrangementAxis_019e2391-9355-7cbb-8527-edcc56fa091f" xlink:to="loc_us-gaap_CollectiveBargainingArrangementDomain_019e2391-9355-7cbb-8527-edcc56fa091f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollectiveBargainingArrangementDomain_019e2391-9355-7589-9a56-17ed3acd58d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollectiveBargainingArrangementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CollectiveBargainingArrangementAxis_019e2391-9355-7cbb-8527-edcc56fa091f" xlink:to="loc_us-gaap_CollectiveBargainingArrangementDomain_019e2391-9355-7589-9a56-17ed3acd58d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_CollectiveBargainingArrangementEmployeeGroupPilotsMember_019e2391-9355-74b2-880e-546c235e34a9" xlink:href="fron-20260630.xsd#fron_CollectiveBargainingArrangementEmployeeGroupPilotsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019e2391-9355-7589-9a56-17ed3acd58d4" xlink:to="loc_fron_CollectiveBargainingArrangementEmployeeGroupPilotsMember_019e2391-9355-74b2-880e-546c235e34a9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_CollectiveBargainingArrangementEmployeeGroupFlightAttendantsMember_019e2391-9355-7314-b963-d9ef323246ef" xlink:href="fron-20260630.xsd#fron_CollectiveBargainingArrangementEmployeeGroupFlightAttendantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019e2391-9355-7589-9a56-17ed3acd58d4" xlink:to="loc_fron_CollectiveBargainingArrangementEmployeeGroupFlightAttendantsMember_019e2391-9355-7314-b963-d9ef323246ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_CollectiveBargainingArrangementEmployeeGroupAircraftTechniciansMember_019e2391-9355-72b2-9acc-a66ff683a870" xlink:href="fron-20260630.xsd#fron_CollectiveBargainingArrangementEmployeeGroupAircraftTechniciansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019e2391-9355-7589-9a56-17ed3acd58d4" xlink:to="loc_fron_CollectiveBargainingArrangementEmployeeGroupAircraftTechniciansMember_019e2391-9355-72b2-9acc-a66ff683a870" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_CollectiveBargainingArrangementEmployeeGroupAircraftAppearanceAgentsMember_019e2391-9355-7cca-8285-8405277992a2" xlink:href="fron-20260630.xsd#fron_CollectiveBargainingArrangementEmployeeGroupAircraftAppearanceAgentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019e2391-9355-7589-9a56-17ed3acd58d4" xlink:to="loc_fron_CollectiveBargainingArrangementEmployeeGroupAircraftAppearanceAgentsMember_019e2391-9355-7cca-8285-8405277992a2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_CollectiveBargainingArrangementEmployeeGroupDispatchersMember_019e2391-9355-7f19-bd70-c82850a36dbf" xlink:href="fron-20260630.xsd#fron_CollectiveBargainingArrangementEmployeeGroupDispatchersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019e2391-9355-7589-9a56-17ed3acd58d4" xlink:to="loc_fron_CollectiveBargainingArrangementEmployeeGroupDispatchersMember_019e2391-9355-7f19-bd70-c82850a36dbf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_CollectiveBargainingArrangementEmployeeGroupMaterialSpecialistsMember_019e2391-9355-7c9d-8fd2-98332f2ede75" xlink:href="fron-20260630.xsd#fron_CollectiveBargainingArrangementEmployeeGroupMaterialSpecialistsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019e2391-9355-7589-9a56-17ed3acd58d4" xlink:to="loc_fron_CollectiveBargainingArrangementEmployeeGroupMaterialSpecialistsMember_019e2391-9355-7c9d-8fd2-98332f2ede75" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_CollectiveBargainingArrangementEmployeeGroupMaintenanceControllersMember_019e2391-9355-7c72-b926-a2b8f5850217" xlink:href="fron-20260630.xsd#fron_CollectiveBargainingArrangementEmployeeGroupMaintenanceControllersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollectiveBargainingArrangementDomain_019e2391-9355-7589-9a56-17ed3acd58d4" xlink:to="loc_fron_CollectiveBargainingArrangementEmployeeGroupMaintenanceControllersMember_019e2391-9355-7c72-b926-a2b8f5850217" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementToAllEntitysEmployeesPercentage_019e2391-9355-7f76-a9a8-aae4dbdc4c7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementToAllEntitysEmployeesPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MultiemployerPlansLineItems_019e2391-9355-741d-9dcf-c605b7f25e44" xlink:to="loc_us-gaap_MultiemployerPlanPensionSignificantEmployeesCoveredByCollectiveBargainingArrangementToAllEntitysEmployeesPercentage_019e2391-9355-7f76-a9a8-aae4dbdc4c7c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/IncomeTaxesDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#IncomeTaxesDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/IncomeTaxesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsLineItems_019e2391-9355-7477-b1b5-1aac43063e60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLossCarryforwardsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsTable_019e2391-9355-7e22-b56e-34610a1baec8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLossCarryforwardsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_019e2391-9355-7477-b1b5-1aac43063e60" xlink:to="loc_us-gaap_OperatingLossCarryforwardsTable_019e2391-9355-7e22-b56e-34610a1baec8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019e2391-9355-7f31-8412-bda5f36aa3cc" 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_OperatingLossCarryforwardsTable_019e2391-9355-7e22-b56e-34610a1baec8" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019e2391-9355-7f31-8412-bda5f36aa3cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019e2391-9355-7f31-8412-bda5f36aa3cc_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_019e2391-9355-7f31-8412-bda5f36aa3cc" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019e2391-9355-7f31-8412-bda5f36aa3cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019e2391-9355-77c6-87b9-d532b45a3310" 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_019e2391-9355-7f31-8412-bda5f36aa3cc" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019e2391-9355-77c6-87b9-d532b45a3310" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_019e2391-9355-7bd1-a02c-12075693871e" 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_019e2391-9355-77c6-87b9-d532b45a3310" xlink:to="loc_us-gaap_DomesticCountryMember_019e2391-9355-7bd1-a02c-12075693871e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_019e2391-9355-74e8-8d8a-05d190d1fb96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019e2391-9355-77c6-87b9-d532b45a3310" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_019e2391-9355-74e8-8d8a-05d190d1fb96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCountryMember_019e2391-9355-772d-a520-bc98c68214c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019e2391-9355-77c6-87b9-d532b45a3310" xlink:to="loc_us-gaap_ForeignCountryMember_019e2391-9355-772d-a520-bc98c68214c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_019e2391-9355-780a-bf2c-f18090a9a1bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_019e2391-9355-7477-b1b5-1aac43063e60" xlink:to="loc_us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_019e2391-9355-780a-bf2c-f18090a9a1bd" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/FairValueMeasurementsScheduleofCarryingAmountsandEstimatedFairValuesoftheCompanysDebtDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#FairValueMeasurementsScheduleofCarryingAmountsandEstimatedFairValuesoftheCompanysDebtDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/FairValueMeasurementsScheduleofCarryingAmountsandEstimatedFairValuesoftheCompanysDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e2391-9355-7fbf-97a1-767a6552d3a3" 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_019e2391-9355-712a-abda-c0501551b590" 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_019e2391-9355-7fbf-97a1-767a6552d3a3" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e2391-9355-712a-abda-c0501551b590" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e2391-9355-7004-abe2-b7c5f579c071" 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e2391-9355-712a-abda-c0501551b590" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e2391-9355-7004-abe2-b7c5f579c071" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-7004-abe2-b7c5f579c071_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_019e2391-9355-7004-abe2-b7c5f579c071" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-7004-abe2-b7c5f579c071_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-788d-b93d-868d405f2fe3" 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_019e2391-9355-7004-abe2-b7c5f579c071" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-788d-b93d-868d405f2fe3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_PreDeliveryCreditFacilityMember_019e2391-9355-72ee-ad39-9ef5c0bedf30" xlink:href="fron-20260630.xsd#fron_PreDeliveryCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-788d-b93d-868d405f2fe3" xlink:to="loc_fron_PreDeliveryCreditFacilityMember_019e2391-9355-72ee-ad39-9ef5c0bedf30" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_ClassA1EnhancedEquipmentTrustCertificatesMember_019e2391-9355-70a2-8456-932f60f99447" xlink:href="fron-20260630.xsd#fron_ClassA1EnhancedEquipmentTrustCertificatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-788d-b93d-868d405f2fe3" xlink:to="loc_fron_ClassA1EnhancedEquipmentTrustCertificatesMember_019e2391-9355-70a2-8456-932f60f99447" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_AffinityCardAdvancePurchaseMember_019e2391-9355-7555-ad51-a334d6de87ce" xlink:href="fron-20260630.xsd#fron_AffinityCardAdvancePurchaseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-788d-b93d-868d405f2fe3" xlink:to="loc_fron_AffinityCardAdvancePurchaseMember_019e2391-9355-7555-ad51-a334d6de87ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_PayrollSupportProgramPromissoryNoteMember_019e2391-9355-7183-af3a-5d8e259731de" xlink:href="fron-20260630.xsd#fron_PayrollSupportProgramPromissoryNoteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e2391-9355-788d-b93d-868d405f2fe3" xlink:to="loc_fron_PayrollSupportProgramPromissoryNoteMember_019e2391-9355-7183-af3a-5d8e259731de" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019e2391-9355-7a77-ac02-7d9e52c777b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e2391-9355-712a-abda-c0501551b590" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019e2391-9355-7a77-ac02-7d9e52c777b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2391-9355-7a77-ac02-7d9e52c777b3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019e2391-9355-7a77-ac02-7d9e52c777b3" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2391-9355-7a77-ac02-7d9e52c777b3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019e2391-9355-75c6-b122-098ca3c6c865" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019e2391-9355-7a77-ac02-7d9e52c777b3" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019e2391-9355-75c6-b122-098ca3c6c865" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2391-9355-7f1d-85fd-57dea0193343" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019e2391-9355-75c6-b122-098ca3c6c865" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2391-9355-7f1d-85fd-57dea0193343" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019e2391-9355-78da-b13e-90d5d1321eda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2391-9355-7f1d-85fd-57dea0193343" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019e2391-9355-78da-b13e-90d5d1321eda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019e2391-9355-7a29-90e3-93434a4d9a30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019e2391-9355-7f1d-85fd-57dea0193343" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019e2391-9355-7a29-90e3-93434a4d9a30" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019e2391-9355-713f-b1c1-8fd6d12299c8" 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019e2391-9355-712a-abda-c0501551b590" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019e2391-9355-713f-b1c1-8fd6d12299c8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-713f-b1c1-8fd6d12299c8_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_019e2391-9355-713f-b1c1-8fd6d12299c8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-713f-b1c1-8fd6d12299c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-7593-9486-a1271528363b" 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_019e2391-9355-713f-b1c1-8fd6d12299c8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-7593-9486-a1271528363b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019e2391-9355-757b-bec0-d6d4b921469e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-7593-9486-a1271528363b" xlink:to="loc_us-gaap_SecuredDebtMember_019e2391-9355-757b-bec0-d6d4b921469e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019e2391-9355-785b-a51f-84a282b077ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019e2391-9355-7593-9486-a1271528363b" xlink:to="loc_us-gaap_UnsecuredDebtMember_019e2391-9355-785b-a51f-84a282b077ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFairValue_019e2391-9355-73ee-b659-b4d87ea3fe8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019e2391-9355-7fbf-97a1-767a6552d3a3" xlink:to="loc_us-gaap_DebtInstrumentFairValue_019e2391-9355-73ee-b659-b4d87ea3fe8e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.flyfrontier.com/role/FairValueMeasurementsScheduleofFairValueofAssetsandLiabilitiesMeasuredatFairValueDetails" xlink:type="simple" xlink:href="fron-20260630.xsd#FairValueMeasurementsScheduleofFairValueofAssetsandLiabilitiesMeasuredatFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.flyfrontier.com/role/FairValueMeasurementsScheduleofFairValueofAssetsandLiabilitiesMeasuredatFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019e2391-9355-7f8a-abd4-46769a410846" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e2391-9355-7da0-b7c5-35ed8ec93412" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019e2391-9355-7f8a-abd4-46769a410846" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019e2391-9355-7da0-b7c5-35ed8ec93412" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2391-9355-7f58-8f7f-c5b50a749cfd" 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_FairValueByBalanceSheetGroupingTable_019e2391-9355-7da0-b7c5-35ed8ec93412" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e2391-9355-7f58-8f7f-c5b50a749cfd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2391-9355-7f58-8f7f-c5b50a749cfd_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_019e2391-9355-7f58-8f7f-c5b50a749cfd" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2391-9355-7f58-8f7f-c5b50a749cfd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2391-9355-76a3-83fe-9360047eec6d" 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_019e2391-9355-7f58-8f7f-c5b50a749cfd" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e2391-9355-76a3-83fe-9360047eec6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019e2391-9355-7f2a-9804-4eaae7619adb" 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_019e2391-9355-76a3-83fe-9360047eec6d" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019e2391-9355-7f2a-9804-4eaae7619adb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019e2391-9355-790a-92d1-e9ee76b5a316" 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_019e2391-9355-76a3-83fe-9360047eec6d" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019e2391-9355-790a-92d1-e9ee76b5a316" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019e2391-9355-76ec-b215-f25694e46478" 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_019e2391-9355-76a3-83fe-9360047eec6d" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019e2391-9355-76ec-b215-f25694e46478" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019e2391-9355-7a7f-a267-bd707110cf8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019e2391-9355-7f8a-abd4-46769a410846" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019e2391-9355-7a7f-a267-bd707110cf8e" xlink:type="arc" order="0"/>
  </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_fron_TrevorStedkeMember_019e2391-940d-7adf-89f3-f445b46a69a1" xlink:href="fron-20260630.xsd#fron_TrevorStedkeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_fron_TrevorStedkeMember_019e2391-940d-7adf-89f3-f445b46a69a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_SteveSchullerMember_019f2387-5b0a-7d06-a9a0-6f65bc96db35" xlink:href="fron-20260630.xsd#fron_SteveSchullerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_fron_SteveSchullerMember_019f2387-5b0a-7d06-a9a0-6f65bc96db35" xlink:type="arc" order="3"/>
  </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_fron_TrevorStedke2025TradingArrangementMember_019f7103-f196-7507-ba82-e012d9267bf3" xlink:href="fron-20260630.xsd#fron_TrevorStedke2025TradingArrangementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllTradingArrangementsMember" xlink:to="loc_fron_TrevorStedke2025TradingArrangementMember_019f7103-f196-7507-ba82-e012d9267bf3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fron_TrevorStedke2026TradingArrangementMember_019f7104-bf73-77d4-bc06-155e16bdb1f4" xlink:href="fron-20260630.xsd#fron_TrevorStedke2026TradingArrangementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllTradingArrangementsMember" xlink:to="loc_fron_TrevorStedke2026TradingArrangementMember_019f7104-bf73-77d4-bc06-155e16bdb1f4" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
