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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:01a03a2a-ac93-716e-b982-7dbe0073842a,g:58d78e2f-65f4-4fff-973e-d871f757c070-->
<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.alx-inc.com/role/ConsolidatedBalanceSheetsUnaudited" xlink:type="simple" xlink:href="alx-20260930.xsd#ConsolidatedBalanceSheetsUnaudited"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedBalanceSheetsUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a03a2a-ad40-7eba-af8a-c7069f5fd25d" 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_01a03a2a-ad40-7f8a-8637-3ea34f3eab36" 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_01a03a2a-ad40-7eba-af8a-c7069f5fd25d" xlink:to="loc_us-gaap_StatementTable_01a03a2a-ad40-7f8a-8637-3ea34f3eab36" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7bcd-af56-8f7e9806aa2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a03a2a-ad40-7f8a-8637-3ea34f3eab36" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7bcd-af56-8f7e9806aa2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7bcd-af56-8f7e9806aa2c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7bcd-af56-8f7e9806aa2c" xlink:to="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7bcd-af56-8f7e9806aa2c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7b35-b80d-9943ee7e8ead" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7bcd-af56-8f7e9806aa2c" xlink:to="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7b35-b80d-9943ee7e8ead" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a03a2a-ad40-76dd-90c9-e65be67a0bed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7b35-b80d-9943ee7e8ead" xlink:to="loc_us-gaap_RelatedPartyMember_01a03a2a-ad40-76dd-90c9-e65be67a0bed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_01a03a2a-ad40-7d19-bca3-e34630a74616" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonrelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7b35-b80d-9943ee7e8ead" xlink:to="loc_us-gaap_NonrelatedPartyMember_01a03a2a-ad40-7d19-bca3-e34630a74616" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a03a2a-ad40-7eba-af8a-c7069f5fd25d" xlink:to="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyAtCostAbstract_01a03a2a-ad40-7466-8cb7-45c9c5ba26c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateInvestmentPropertyAtCostAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyAtCostAbstract_01a03a2a-ad40-7466-8cb7-45c9c5ba26c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Land_01a03a2a-ad40-74fd-95a8-22cc06d4e39b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Land"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateInvestmentPropertyAtCostAbstract_01a03a2a-ad40-7466-8cb7-45c9c5ba26c2" xlink:to="loc_us-gaap_Land_01a03a2a-ad40-74fd-95a8-22cc06d4e39b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingsAndImprovementsGross_01a03a2a-ad40-7968-b2b8-9711a14c3758" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BuildingsAndImprovementsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateInvestmentPropertyAtCostAbstract_01a03a2a-ad40-7466-8cb7-45c9c5ba26c2" xlink:to="loc_us-gaap_BuildingsAndImprovementsGross_01a03a2a-ad40-7968-b2b8-9711a14c3758" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopmentInProcess_01a03a2a-ad40-7c18-be4e-4085bba54547" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DevelopmentInProcess"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateInvestmentPropertyAtCostAbstract_01a03a2a-ad40-7466-8cb7-45c9c5ba26c2" xlink:to="loc_us-gaap_DevelopmentInProcess_01a03a2a-ad40-7c18-be4e-4085bba54547" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyAtCost_01a03a2a-ad40-728b-aef9-a858a37187b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateInvestmentPropertyAtCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateInvestmentPropertyAtCostAbstract_01a03a2a-ad40-7466-8cb7-45c9c5ba26c2" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyAtCost_01a03a2a-ad40-728b-aef9-a858a37187b5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyAccumulatedDepreciation_01a03a2a-ad40-7602-bfab-325dd13d3eb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateInvestmentPropertyAccumulatedDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyAccumulatedDepreciation_01a03a2a-ad40-7602-bfab-325dd13d3eb5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateInvestmentPropertyNet_01a03a2a-ad40-76af-a0d9-1a35648e5fb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateInvestmentPropertyNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:to="loc_us-gaap_RealEstateInvestmentPropertyNet_01a03a2a-ad40-76af-a0d9-1a35648e5fb0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a03a2a-ad40-7f28-8c24-fe627f83288d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a03a2a-ad40-7f28-8c24-fe627f83288d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalents_01a03a2a-ad40-7c19-b8ad-6132572cc421" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalents_01a03a2a-ad40-7c19-b8ad-6132572cc421" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNet_01a03a2a-ad40-7ea4-bc68-23dc2b5ae4e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:to="loc_us-gaap_AccountsReceivableNet_01a03a2a-ad40-7ea4-bc68-23dc2b5ae4e8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRentReceivablesNet_01a03a2a-ad40-719d-934a-a27bfb05e1ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredRentReceivablesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:to="loc_us-gaap_DeferredRentReceivablesNet_01a03a2a-ad40-719d-934a-a27bfb05e1ce" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCostsLeasingNet_01a03a2a-ad40-7a5c-94bf-038c179f21c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredCostsLeasingNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:to="loc_us-gaap_DeferredCostsLeasingNet_01a03a2a-ad40-7a5c-94bf-038c179f21c5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssets_01a03a2a-ad40-78f8-bb6b-6e2c1c2c246c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:to="loc_us-gaap_OtherAssets_01a03a2a-ad40-78f8-bb6b-6e2c1c2c246c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a03a2a-ad40-701b-81d6-9bf9f5847521" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7319-8b6f-b23d51e8c0d5" xlink:to="loc_us-gaap_Assets_01a03a2a-ad40-701b-81d6-9bf9f5847521" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a03a2a-ad40-7eba-af8a-c7069f5fd25d" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayable_01a03a2a-ad40-732f-877a-d2744cf540ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_NotesPayable_01a03a2a-ad40-732f-877a-d2744cf540ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilities_01a03a2a-ad40-78de-b738-a4027629c3f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_OtherLiabilities_01a03a2a-ad40-78de-b738-a4027629c3f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent_01a03a2a-ad40-7ef5-a2e8-05101219774b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent_01a03a2a-ad40-7ef5-a2e8-05101219774b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncentiveFromLessor_01a03a2a-ad40-7899-9f13-4a0eba158b1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncentiveFromLessor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_IncentiveFromLessor_01a03a2a-ad40-7899-9f13-4a0eba158b1b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_01a03a2a-ad40-7211-b4f0-3fb3965da2f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_Liabilities_01a03a2a-ad40-7211-b4f0-3fb3965da2f1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_01a03a2a-ad40-7e97-9594-b34732131fd6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_CommitmentsAndContingencies_01a03a2a-ad40-7e97-9594-b34732131fd6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValueOutstanding_01a03a2a-ad40-7966-9f7f-38b4c08f540d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockValueOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_PreferredStockValueOutstanding_01a03a2a-ad40-7966-9f7f-38b4c08f540d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValueOutstanding_01a03a2a-ad40-72f2-8f7e-ba395e814ced" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValueOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_CommonStockValueOutstanding_01a03a2a-ad40-72f2-8f7e-ba395e814ced" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_01a03a2a-ad40-72ca-8fee-fd504d62aee9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_AdditionalPaidInCapital_01a03a2a-ad40-72ca-8fee-fd504d62aee9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a03a2a-ad40-7e07-aac4-9a46bd99775e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a03a2a-ad40-7e07-aac4-9a46bd99775e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a03a2a-ad40-7207-bc29-2ffb6b7d4a94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a03a2a-ad40-7207-bc29-2ffb6b7d4a94" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityBeforeTreasuryStock_01a03a2a-ad40-707d-9a57-9668429ba238" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityBeforeTreasuryStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_StockholdersEquityBeforeTreasuryStock_01a03a2a-ad40-707d-9a57-9668429ba238" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonValue_01a03a2a-ad40-7504-81f0-d29cd646724b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_TreasuryStockCommonValue_01a03a2a-ad40-7504-81f0-d29cd646724b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a03a2a-ad40-7c1d-9cfa-35f93558e935" 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_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_StockholdersEquity_01a03a2a-ad40-7c1d-9cfa-35f93558e935" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_01a03a2a-ad40-733b-9de6-3d12810cc273" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a03a2a-ad40-75ef-89cf-10463630cc3d" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_01a03a2a-ad40-733b-9de6-3d12810cc273" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedStatementsofIncomeUnauditedParenthetical" xlink:type="simple" xlink:href="alx-20260930.xsd#ConsolidatedStatementsofIncomeUnauditedParenthetical"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsofIncomeUnauditedParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a03a2a-ad40-7766-96b7-2e618ee7a54a" 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_01a03a2a-ad40-77ea-ad34-d2e7d1df5ba1" 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_01a03a2a-ad40-7766-96b7-2e618ee7a54a" xlink:to="loc_us-gaap_StatementTable_01a03a2a-ad40-77ea-ad34-d2e7d1df5ba1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7030-9123-189c61e7143b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a03a2a-ad40-77ea-ad34-d2e7d1df5ba1" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7030-9123-189c61e7143b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7030-9123-189c61e7143b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7030-9123-189c61e7143b" xlink:to="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7030-9123-189c61e7143b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7f36-9bbd-bf3cf2ddf3fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7030-9123-189c61e7143b" xlink:to="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7f36-9bbd-bf3cf2ddf3fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a03a2a-ad40-71e5-98f4-769718e9f2b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7f36-9bbd-bf3cf2ddf3fe" xlink:to="loc_us-gaap_RelatedPartyMember_01a03a2a-ad40-71e5-98f4-769718e9f2b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpenses_01a03a2a-ad40-77f9-9bc4-4a2e0d1116ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingCostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a03a2a-ad40-7766-96b7-2e618ee7a54a" xlink:to="loc_us-gaap_OperatingCostsAndExpenses_01a03a2a-ad40-77f9-9bc4-4a2e0d1116ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_01a03a2a-ad40-7b18-9678-3789ecc97633" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a03a2a-ad40-7766-96b7-2e618ee7a54a" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_01a03a2a-ad40-7b18-9678-3789ecc97633" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedStatementsofChangesinEquityUnaudited" xlink:type="simple" xlink:href="alx-20260930.xsd#ConsolidatedStatementsofChangesinEquityUnaudited"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsofChangesinEquityUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a03a2a-ad40-7531-9797-b3ba7e668d60" 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_01a03a2a-ad40-79a0-999f-4feacc4638de" 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_01a03a2a-ad40-7531-9797-b3ba7e668d60" xlink:to="loc_us-gaap_StatementTable_01a03a2a-ad40-79a0-999f-4feacc4638de" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a03a2a-ad40-7aae-ac37-a9b39f527609" 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_01a03a2a-ad40-79a0-999f-4feacc4638de" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a03a2a-ad40-7aae-ac37-a9b39f527609" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a03a2a-ad40-7aae-ac37-a9b39f527609_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_01a03a2a-ad40-7aae-ac37-a9b39f527609" xlink:to="loc_us-gaap_EquityComponentDomain_01a03a2a-ad40-7aae-ac37-a9b39f527609_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a03a2a-ad40-74b9-b1eb-c1a7f1721cf2" 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_01a03a2a-ad40-7aae-ac37-a9b39f527609" xlink:to="loc_us-gaap_EquityComponentDomain_01a03a2a-ad40-74b9-b1eb-c1a7f1721cf2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a03a2a-ad40-7d38-97f8-d95f68c1dbb1" 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_01a03a2a-ad40-74b9-b1eb-c1a7f1721cf2" xlink:to="loc_us-gaap_CommonStockMember_01a03a2a-ad40-7d38-97f8-d95f68c1dbb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_01a03a2a-ad40-75a9-b85a-7b1308b6d82e" 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_01a03a2a-ad40-74b9-b1eb-c1a7f1721cf2" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_01a03a2a-ad40-75a9-b85a-7b1308b6d82e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_01a03a2a-ad40-73b1-b37f-6421e66354b1" 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_01a03a2a-ad40-74b9-b1eb-c1a7f1721cf2" xlink:to="loc_us-gaap_RetainedEarningsMember_01a03a2a-ad40-73b1-b37f-6421e66354b1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a03a2a-ad40-794f-b671-ada4006ad6c0" 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_01a03a2a-ad40-74b9-b1eb-c1a7f1721cf2" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a03a2a-ad40-794f-b671-ada4006ad6c0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_01a03a2a-ad40-7cf2-8ca7-370063a2dc5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a03a2a-ad40-74b9-b1eb-c1a7f1721cf2" xlink:to="loc_us-gaap_TreasuryStockCommonMember_01a03a2a-ad40-7cf2-8ca7-370063a2dc5b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03a2a-ad40-71ab-8b18-ade5372ab88d" 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_01a03a2a-ad40-7531-9797-b3ba7e668d60" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03a2a-ad40-71ab-8b18-ade5372ab88d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_01a03a2a-ad40-7ad7-8f89-0e2f8cc9313a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03a2a-ad40-71ab-8b18-ade5372ab88d" xlink:to="loc_us-gaap_CommonStockSharesIssued_01a03a2a-ad40-7ad7-8f89-0e2f8cc9313a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a03a2a-ad40-791f-95f9-2237d86fa2b2" 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_01a03a2a-ad40-71ab-8b18-ade5372ab88d" xlink:to="loc_us-gaap_StockholdersEquity_01a03a2a-ad40-791f-95f9-2237d86fa2b2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a03a2a-ad40-7585-9685-f8ab53c6bb44" 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_01a03a2a-ad40-71ab-8b18-ade5372ab88d" xlink:to="loc_us-gaap_NetIncomeLoss_01a03a2a-ad40-7585-9685-f8ab53c6bb44" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_01a03a2a-ad40-719f-bac8-c14925071f52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03a2a-ad40-71ab-8b18-ade5372ab88d" xlink:to="loc_us-gaap_DividendsCommonStockCash_01a03a2a-ad40-719f-bac8-c14925071f52" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_01a03a2a-ad40-7610-9083-cd8794982dab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03a2a-ad40-71ab-8b18-ade5372ab88d" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_01a03a2a-ad40-7610-9083-cd8794982dab" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition_01a03a2a-ad40-71a3-84a2-25d86cc5a4f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a03a2a-ad40-71ab-8b18-ade5372ab88d" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition_01a03a2a-ad40-71a3-84a2-25d86cc5a4f4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_01a03a2a-ad40-75ca-944d-5197c8620625" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a03a2a-ad40-71f2-9d62-6fe1389378fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/ConsolidatedStatementsofCashFlowsUnauditedParenthetical" xlink:type="simple" xlink:href="alx-20260930.xsd#ConsolidatedStatementsofCashFlowsUnauditedParenthetical"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/ConsolidatedStatementsofCashFlowsUnauditedParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a03a2a-ad40-7564-b2f9-c1b1c09fe40b" 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_01a03a2a-ad40-700e-98e9-30e1d5c2acf6" 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_01a03a2a-ad40-7564-b2f9-c1b1c09fe40b" xlink:to="loc_us-gaap_StatementTable_01a03a2a-ad40-700e-98e9-30e1d5c2acf6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7f85-bff1-0cbf60ef29af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a03a2a-ad40-700e-98e9-30e1d5c2acf6" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7f85-bff1-0cbf60ef29af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7f85-bff1-0cbf60ef29af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7f85-bff1-0cbf60ef29af" xlink:to="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7f85-bff1-0cbf60ef29af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-76d4-8191-6d4504bf4cc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7f85-bff1-0cbf60ef29af" xlink:to="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-76d4-8191-6d4504bf4cc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a03a2a-ad40-7273-ab07-8ce385b033bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-76d4-8191-6d4504bf4cc3" xlink:to="loc_us-gaap_RelatedPartyMember_01a03a2a-ad40-7273-ab07-8ce385b033bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_NonCashAdditionsToRealEstate_01a03a2a-ad40-7dfa-b0ac-f3945cff4ba7" xlink:href="alx-20260930.xsd#alx_NonCashAdditionsToRealEstate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a03a2a-ad40-7564-b2f9-c1b1c09fe40b" xlink:to="loc_alx_NonCashAdditionsToRealEstate_01a03a2a-ad40-7dfa-b0ac-f3945cff4ba7" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/RevenueRecognitionScheduleofRevenueDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#RevenueRecognitionScheduleofRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RevenueRecognitionScheduleofRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7739-901a-ff5fd2491985" 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_01a03a2a-ad40-7445-91c1-1459113da37f" 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_01a03a2a-ad40-7739-901a-ff5fd2491985" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_01a03a2a-ad40-7445-91c1-1459113da37f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a03a2a-ad40-70d6-b36e-aff0037e220a" 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_01a03a2a-ad40-7445-91c1-1459113da37f" xlink:to="loc_srt_ProductOrServiceAxis_01a03a2a-ad40-70d6-b36e-aff0037e220a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a03a2a-ad40-70d6-b36e-aff0037e220a_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_01a03a2a-ad40-70d6-b36e-aff0037e220a" xlink:to="loc_srt_ProductsAndServicesDomain_01a03a2a-ad40-70d6-b36e-aff0037e220a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a03a2a-ad40-7056-8cf9-db7a8dded2b9" 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_01a03a2a-ad40-70d6-b36e-aff0037e220a" xlink:to="loc_srt_ProductsAndServicesDomain_01a03a2a-ad40-7056-8cf9-db7a8dded2b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParkingMember_01a03a2a-ad40-774b-9b06-9e7c24c027cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ParkingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a03a2a-ad40-7056-8cf9-db7a8dded2b9" xlink:to="loc_us-gaap_ParkingMember_01a03a2a-ad40-774b-9b06-9e7c24c027cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DirectServicesMember_01a03a2a-ad40-78ed-84f2-8c9347e426f4" xlink:href="alx-20260930.xsd#alx_DirectServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a03a2a-ad40-7056-8cf9-db7a8dded2b9" xlink:to="loc_alx_DirectServicesMember_01a03a2a-ad40-78ed-84f2-8c9347e426f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLeaseIncome_01a03a2a-ad40-79fe-a204-5cb759d8e311" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLeaseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7739-901a-ff5fd2491985" xlink:to="loc_us-gaap_OperatingLeaseLeaseIncome_01a03a2a-ad40-79fe-a204-5cb759d8e311" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a03a2a-ad40-7597-a6b9-30ce9820b0a4" 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_01a03a2a-ad40-7739-901a-ff5fd2491985" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a03a2a-ad40-7597-a6b9-30ce9820b0a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a03a2a-ad40-715b-b679-e91c8662ace5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7739-901a-ff5fd2491985" xlink:to="loc_us-gaap_Revenues_01a03a2a-ad40-715b-b679-e91c8662ace5" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/RevenueRecognitionNarrativeDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#RevenueRecognitionNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RevenueRecognitionNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7eec-a950-25c18dda5234" 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_01a03a2a-ad40-7d86-bc9f-65a11ca46406" 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_01a03a2a-ad40-7eec-a950-25c18dda5234" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_01a03a2a-ad40-7d86-bc9f-65a11ca46406" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_01a03a2a-ad40-7ceb-a1dd-4f3b6200589d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_01a03a2a-ad40-7d86-bc9f-65a11ca46406" xlink:to="loc_srt_MajorCustomersAxis_01a03a2a-ad40-7ceb-a1dd-4f3b6200589d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a03a2a-ad40-7ceb-a1dd-4f3b6200589d_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_01a03a2a-ad40-7ceb-a1dd-4f3b6200589d" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a03a2a-ad40-7ceb-a1dd-4f3b6200589d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a03a2a-ad40-7932-a7b7-5849b109f611" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_01a03a2a-ad40-7ceb-a1dd-4f3b6200589d" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a03a2a-ad40-7932-a7b7-5849b109f611" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_BloombergL.P.Member_01a03a2a-ad40-7985-a93c-c410df3bb689" xlink:href="alx-20260930.xsd#alx_BloombergL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_01a03a2a-ad40-7932-a7b7-5849b109f611" xlink:to="loc_alx_BloombergL.P.Member_01a03a2a-ad40-7985-a93c-c410df3bb689" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7730-90a8-6d979cbabe80" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_01a03a2a-ad40-7d86-bc9f-65a11ca46406" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7730-90a8-6d979cbabe80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-7730-90a8-6d979cbabe80_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7730-90a8-6d979cbabe80" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-7730-90a8-6d979cbabe80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-7335-9de3-75ab224ea961" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7730-90a8-6d979cbabe80" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-7335-9de3-75ab224ea961" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_A731LexingtonAvenuePropertyMember_01a03a2a-ad40-7a91-901b-da41a47d9e62" xlink:href="alx-20260930.xsd#alx_A731LexingtonAvenuePropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-7335-9de3-75ab224ea961" xlink:to="loc_alx_A731LexingtonAvenuePropertyMember_01a03a2a-ad40-7a91-901b-da41a47d9e62" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RegoParkShoppingCenterMember_01a03a2a-ad40-7014-949b-e010021c0a82" xlink:href="alx-20260930.xsd#alx_RegoParkShoppingCenterMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-7335-9de3-75ab224ea961" xlink:to="loc_alx_RegoParkShoppingCenterMember_01a03a2a-ad40-7014-949b-e010021c0a82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a03a2a-ad40-7339-bd55-b8ccc5fbd215" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_01a03a2a-ad40-7d86-bc9f-65a11ca46406" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a03a2a-ad40-7339-bd55-b8ccc5fbd215" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a03a2a-ad40-7339-bd55-b8ccc5fbd215_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a03a2a-ad40-7339-bd55-b8ccc5fbd215" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a03a2a-ad40-7339-bd55-b8ccc5fbd215_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a03a2a-ad40-7001-abb6-1f3a07fbcebb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a03a2a-ad40-7339-bd55-b8ccc5fbd215" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a03a2a-ad40-7001-abb6-1f3a07fbcebb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_01a03a2a-ad40-7b39-bfc5-d6e1950ed314" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a03a2a-ad40-7001-abb6-1f3a07fbcebb" xlink:to="loc_us-gaap_SalesRevenueNetMember_01a03a2a-ad40-7b39-bfc5-d6e1950ed314" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a03a2a-ad40-76fa-8651-66d1510ceb4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_01a03a2a-ad40-7d86-bc9f-65a11ca46406" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a03a2a-ad40-76fa-8651-66d1510ceb4d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a03a2a-ad40-76fa-8651-66d1510ceb4d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a03a2a-ad40-76fa-8651-66d1510ceb4d" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a03a2a-ad40-76fa-8651-66d1510ceb4d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a03a2a-ad40-7b81-a2d4-f5a4916eec32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a03a2a-ad40-76fa-8651-66d1510ceb4d" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a03a2a-ad40-7b81-a2d4-f5a4916eec32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_01a03a2a-ad40-7dcf-b149-3154022c10d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a03a2a-ad40-7b81-a2d4-f5a4916eec32" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_01a03a2a-ad40-7dcf-b149-3154022c10d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a03a2a-ad40-7395-9f34-051b22ef5fa8" 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_DisaggregationOfRevenueTable_01a03a2a-ad40-7d86-bc9f-65a11ca46406" xlink:to="loc_srt_RangeAxis_01a03a2a-ad40-7395-9f34-051b22ef5fa8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03a2a-ad40-7395-9f34-051b22ef5fa8_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_01a03a2a-ad40-7395-9f34-051b22ef5fa8" xlink:to="loc_srt_RangeMember_01a03a2a-ad40-7395-9f34-051b22ef5fa8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03a2a-ad40-7124-a9ed-35f401c87d96" 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_01a03a2a-ad40-7395-9f34-051b22ef5fa8" xlink:to="loc_srt_RangeMember_01a03a2a-ad40-7124-a9ed-35f401c87d96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a03a2a-ad40-7df5-8d27-32fe4cbac317" 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_01a03a2a-ad40-7124-a9ed-35f401c87d96" xlink:to="loc_srt_MaximumMember_01a03a2a-ad40-7df5-8d27-32fe4cbac317" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a03a2a-ad40-7565-89c6-2d96591d9341" 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_01a03a2a-ad40-7124-a9ed-35f401c87d96" xlink:to="loc_srt_MinimumMember_01a03a2a-ad40-7565-89c6-2d96591d9341" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_01a03a2a-ad40-7255-9115-2dd910da81d1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_01a03a2a-ad40-7d86-bc9f-65a11ca46406" xlink:to="loc_srt_StatementScenarioAxis_01a03a2a-ad40-7255-9115-2dd910da81d1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_01a03a2a-ad40-7255-9115-2dd910da81d1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_01a03a2a-ad40-7255-9115-2dd910da81d1" xlink:to="loc_srt_ScenarioUnspecifiedDomain_01a03a2a-ad40-7255-9115-2dd910da81d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_01a03a2a-ad40-7f18-b7d0-2ea04e18ea7f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_01a03a2a-ad40-7255-9115-2dd910da81d1" xlink:to="loc_srt_ScenarioUnspecifiedDomain_01a03a2a-ad40-7f18-b7d0-2ea04e18ea7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_01a03a2a-ad40-71cb-818d-49891a0873c7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_01a03a2a-ad40-7f18-b7d0-2ea04e18ea7f" xlink:to="loc_srt_ScenarioForecastMember_01a03a2a-ad40-71cb-818d-49891a0873c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AreaOfRealEstateProperty_01a03a2a-ad40-7dbf-9c4e-e1b2bb89a2b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AreaOfRealEstateProperty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7eec-a950-25c18dda5234" xlink:to="loc_us-gaap_AreaOfRealEstateProperty_01a03a2a-ad40-7dbf-9c4e-e1b2bb89a2b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a03a2a-ad40-7056-aef9-5d07ab628f5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7eec-a950-25c18dda5234" xlink:to="loc_us-gaap_Revenues_01a03a2a-ad40-7056-aef9-5d07ab628f5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a03a2a-ad40-7b9e-9533-2255a3757e61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7eec-a950-25c18dda5234" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a03a2a-ad40-7b9e-9533-2255a3757e61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LessorLeaseTerm_01a03a2a-ad40-748e-892b-84e15f2874e7" xlink:href="alx-20260930.xsd#alx_LessorLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7eec-a950-25c18dda5234" xlink:to="loc_alx_LessorLeaseTerm_01a03a2a-ad40-748e-892b-84e15f2874e7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncentiveFromLessor_01a03a2a-ad40-7478-ae71-753d342dc0ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncentiveFromLessor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7eec-a950-25c18dda5234" xlink:to="loc_us-gaap_IncentiveFromLessor_01a03a2a-ad40-7478-ae71-753d342dc0ff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_IncentiveAssetFromLessor_01a03a2a-ad40-7755-a18d-79814de2972b" xlink:href="alx-20260930.xsd#alx_IncentiveAssetFromLessor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7eec-a950-25c18dda5234" xlink:to="loc_alx_IncentiveAssetFromLessor_01a03a2a-ad40-7755-a18d-79814de2972b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RentAbatementAmount_01a03a2a-ad40-7508-83f2-0333e25a2108" xlink:href="alx-20260930.xsd#alx_RentAbatementAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7eec-a950-25c18dda5234" xlink:to="loc_alx_RentAbatementAmount_01a03a2a-ad40-7508-83f2-0333e25a2108" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_TenantFundByCorrespondingAmount_01a03a2a-ad40-7010-814f-d0f413f16816" xlink:href="alx-20260930.xsd#alx_TenantFundByCorrespondingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7eec-a950-25c18dda5234" xlink:to="loc_alx_TenantFundByCorrespondingAmount_01a03a2a-ad40-7010-814f-d0f413f16816" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LessorOperatingLeaseEarlyContractTerminationOptionPayment_01a03a2a-ad40-7c4d-a9fc-09239ec83276" xlink:href="alx-20260930.xsd#alx_LessorOperatingLeaseEarlyContractTerminationOptionPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7eec-a950-25c18dda5234" xlink:to="loc_alx_LessorOperatingLeaseEarlyContractTerminationOptionPayment_01a03a2a-ad40-7c4d-a9fc-09239ec83276" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseTermOfContract_01a03a2a-ad40-754c-9a5d-ecff9b49bcef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a03a2a-ad40-7eec-a950-25c18dda5234" xlink:to="loc_us-gaap_LesseeOperatingLeaseTermOfContract_01a03a2a-ad40-754c-9a5d-ecff9b49bcef" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/RealEstateSaleDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#RealEstateSaleDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RealEstateSaleDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a03a2a-ad40-735c-86ec-409c89a4fe74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a03a2a-ad40-7fbb-bb55-ec8d4c4b69bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a03a2a-ad40-735c-86ec-409c89a4fe74" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a03a2a-ad40-7fbb-bb55-ec8d4c4b69bd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_01a03a2a-ad40-7e78-97c0-7c312d7569a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a03a2a-ad40-7fbb-bb55-ec8d4c4b69bd" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_01a03a2a-ad40-7e78-97c0-7c312d7569a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a03a2a-ad40-7e78-97c0-7c312d7569a1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a03a2a-ad40-7e78-97c0-7c312d7569a1" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a03a2a-ad40-7e78-97c0-7c312d7569a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a03a2a-ad40-71e3-bef7-cb2b3231c1d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a03a2a-ad40-7e78-97c0-7c312d7569a1" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a03a2a-ad40-71e3-bef7-cb2b3231c1d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_01a197d8-ee30-7a66-9a28-3080045346bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_01a03a2a-ad40-71e3-bef7-cb2b3231c1d5" xlink:to="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_01a197d8-ee30-7a66-9a28-3080045346bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a03a2a-ad40-7e47-a06d-673cf8723d03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_01a03a2a-ad40-7fbb-bb55-ec8d4c4b69bd" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a03a2a-ad40-7e47-a06d-673cf8723d03" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a03a2a-ad40-7e47-a06d-673cf8723d03_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a03a2a-ad40-7e47-a06d-673cf8723d03" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a03a2a-ad40-7e47-a06d-673cf8723d03_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a03a2a-ad40-7afe-a90c-bdbce7711991" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a03a2a-ad40-7e47-a06d-673cf8723d03" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a03a2a-ad40-7afe-a90c-bdbce7711991" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RegoParkIPropertyMember_01a03a2a-ad40-7fc5-b55c-c20a10a4ba7c" xlink:href="alx-20260930.xsd#alx_RegoParkIPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a03a2a-ad40-7afe-a90c-bdbce7711991" xlink:to="loc_alx_RegoParkIPropertyMember_01a03a2a-ad40-7fc5-b55c-c20a10a4ba7c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_01a03a2a-ad40-7874-bfa2-286230661387" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a03a2a-ad40-735c-86ec-409c89a4fe74" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_01a03a2a-ad40-7874-bfa2-286230661387" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDebtNetOfIssuanceCosts_01a03a2a-ad40-7bf5-a273-172a80258abd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromDebtNetOfIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a03a2a-ad40-735c-86ec-409c89a4fe74" xlink:to="loc_us-gaap_ProceedsFromDebtNetOfIssuanceCosts_01a03a2a-ad40-7bf5-a273-172a80258abd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnSalesOfInvestmentRealEstate_01a03a2a-ad40-7fd2-82c2-3db362274f26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnSalesOfInvestmentRealEstate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a03a2a-ad40-735c-86ec-409c89a4fe74" xlink:to="loc_us-gaap_GainsLossesOnSalesOfInvestmentRealEstate_01a03a2a-ad40-7fd2-82c2-3db362274f26" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/RelatedPartyTransactionsNarrativeDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#RelatedPartyTransactionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RelatedPartyTransactionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-795f-aa6b-f74d2c30ced3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-795f-aa6b-f74d2c30ced3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_01a03a2a-ad40-725e-a3c9-a9a221afdafc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-795f-aa6b-f74d2c30ced3" xlink:to="loc_srt_OwnershipAxis_01a03a2a-ad40-725e-a3c9-a9a221afdafc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_01a03a2a-ad40-725e-a3c9-a9a221afdafc_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_01a03a2a-ad40-725e-a3c9-a9a221afdafc" xlink:to="loc_srt_OwnershipDomain_01a03a2a-ad40-725e-a3c9-a9a221afdafc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_01a03a2a-ad40-71d9-a8ea-621446d03d52" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_01a03a2a-ad40-725e-a3c9-a9a221afdafc" xlink:to="loc_srt_OwnershipDomain_01a03a2a-ad40-71d9-a8ea-621446d03d52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_AlexandersInc.Member_01a03a2a-ad40-71c8-a741-00e56260d361" xlink:href="alx-20260930.xsd#alx_AlexandersInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_01a03a2a-ad40-71d9-a8ea-621446d03d52" xlink:to="loc_alx_AlexandersInc.Member_01a03a2a-ad40-71c8-a741-00e56260d361" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7d5a-bd9a-3c3a74037418" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-795f-aa6b-f74d2c30ced3" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7d5a-bd9a-3c3a74037418" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7d5a-bd9a-3c3a74037418_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7d5a-bd9a-3c3a74037418" xlink:to="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7d5a-bd9a-3c3a74037418_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7484-8eec-046b371afa91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a03a2a-ad40-7d5a-bd9a-3c3a74037418" xlink:to="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7484-8eec-046b371afa91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a03a2a-ad40-7572-a757-98160ebcb2ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7484-8eec-046b371afa91" xlink:to="loc_us-gaap_RelatedPartyMember_01a03a2a-ad40-7572-a757-98160ebcb2ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_01a03a2a-ad40-75ca-86d6-47c13021fea3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a03a2a-ad40-7484-8eec-046b371afa91" xlink:to="loc_srt_AffiliatedEntityMember_01a03a2a-ad40-75ca-86d6-47c13021fea3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a03a2a-ad40-7a9d-b1eb-a11e6bb63691" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-795f-aa6b-f74d2c30ced3" xlink:to="loc_dei_LegalEntityAxis_01a03a2a-ad40-7a9d-b1eb-a11e6bb63691" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a03a2a-ad40-7a9d-b1eb-a11e6bb63691_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a03a2a-ad40-7a9d-b1eb-a11e6bb63691" xlink:to="loc_dei_EntityDomain_01a03a2a-ad40-7a9d-b1eb-a11e6bb63691_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a03a2a-ad40-77f8-a37a-a660b384aea1" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a03a2a-ad40-7a9d-b1eb-a11e6bb63691" xlink:to="loc_dei_EntityDomain_01a03a2a-ad40-77f8-a37a-a660b384aea1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_VornadoMember_01a03a2a-ad40-727f-a09c-acba40df44a3" xlink:href="alx-20260930.xsd#alx_VornadoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a03a2a-ad40-77f8-a37a-a660b384aea1" xlink:to="loc_alx_VornadoMember_01a03a2a-ad40-727f-a09c-acba40df44a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-73d4-aea8-b20962bbbf2f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-795f-aa6b-f74d2c30ced3" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-73d4-aea8-b20962bbbf2f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-73d4-aea8-b20962bbbf2f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-73d4-aea8-b20962bbbf2f" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-73d4-aea8-b20962bbbf2f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7693-83df-a2b8ca897481" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-73d4-aea8-b20962bbbf2f" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7693-83df-a2b8ca897481" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RetailSiteMember_01a03a2a-ad40-7e61-8863-9c6537dd0ebd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RetailSiteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7693-83df-a2b8ca897481" xlink:to="loc_srt_RetailSiteMember_01a03a2a-ad40-7e61-8863-9c6537dd0ebd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_OfficeAndRetailSpaceMember_01a03a2a-ad40-7f1c-9baa-87cc4db19db3" xlink:href="alx-20260930.xsd#alx_OfficeAndRetailSpaceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7693-83df-a2b8ca897481" xlink:to="loc_alx_OfficeAndRetailSpaceMember_01a03a2a-ad40-7f1c-9baa-87cc4db19db3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_CommonAreaMember_01a03a2a-ad40-7a47-a6d9-de30bd6aed19" xlink:href="alx-20260930.xsd#alx_CommonAreaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7693-83df-a2b8ca897481" xlink:to="loc_alx_CommonAreaMember_01a03a2a-ad40-7a47-a6d9-de30bd6aed19" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7df3-925c-b58561d858bf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-795f-aa6b-f74d2c30ced3" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7df3-925c-b58561d858bf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-7df3-925c-b58561d858bf_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7df3-925c-b58561d858bf" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-7df3-925c-b58561d858bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-73ef-9599-201a2f3c89da" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7df3-925c-b58561d858bf" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-73ef-9599-201a2f3c89da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RegoParkShoppingCenterMember_01a03a2a-ad40-7a26-89d0-9ad5b4dee25b" xlink:href="alx-20260930.xsd#alx_RegoParkShoppingCenterMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-73ef-9599-201a2f3c89da" xlink:to="loc_alx_RegoParkShoppingCenterMember_01a03a2a-ad40-7a26-89d0-9ad5b4dee25b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LexingtonAvenuePropertyMember_01a03a2a-ad40-7e6d-8186-6d8bf14b92f3" xlink:href="alx-20260930.xsd#alx_LexingtonAvenuePropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-73ef-9599-201a2f3c89da" xlink:to="loc_alx_LexingtonAvenuePropertyMember_01a03a2a-ad40-7e6d-8186-6d8bf14b92f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_01a03a2a-ad40-762b-8bfb-39c20af5890a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-795f-aa6b-f74d2c30ced3" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_01a03a2a-ad40-762b-8bfb-39c20af5890a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-762b-8bfb-39c20af5890a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_01a03a2a-ad40-762b-8bfb-39c20af5890a" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-762b-8bfb-39c20af5890a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7708-9ef7-55330e63b20b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_01a03a2a-ad40-762b-8bfb-39c20af5890a" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7708-9ef7-55330e63b20b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PropertyManagementFeesMember_01a03a2a-ad40-7640-b68f-8d259c68d3c7" xlink:href="alx-20260930.xsd#alx_PropertyManagementFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7708-9ef7-55330e63b20b" xlink:to="loc_alx_PropertyManagementFeesMember_01a03a2a-ad40-7640-b68f-8d259c68d3c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ManagementAndDevelopmentAgreementBaseManagementFeeMember_01a03a2a-ad40-76e8-bd74-ff6b32a5eade" xlink:href="alx-20260930.xsd#alx_ManagementAndDevelopmentAgreementBaseManagementFeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7708-9ef7-55330e63b20b" xlink:to="loc_alx_ManagementAndDevelopmentAgreementBaseManagementFeeMember_01a03a2a-ad40-76e8-bd74-ff6b32a5eade" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DevelopmentFeesMember_01a03a2a-ad40-7ccb-9756-3beef29df4d0" xlink:href="alx-20260930.xsd#alx_DevelopmentFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7708-9ef7-55330e63b20b" xlink:to="loc_alx_DevelopmentFeesMember_01a03a2a-ad40-7ccb-9756-3beef29df4d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LeasingFeesMember_01a03a2a-ad40-70cc-b472-aa08beab48fe" xlink:href="alx-20260930.xsd#alx_LeasingFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7708-9ef7-55330e63b20b" xlink:to="loc_alx_LeasingFeesMember_01a03a2a-ad40-70cc-b472-aa08beab48fe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PropertyManagementCleaningEngineeringParkingAndSecurityFeesMember_01a03a2a-ad40-7f01-8f7d-e79e9a5088b0" xlink:href="alx-20260930.xsd#alx_PropertyManagementCleaningEngineeringParkingAndSecurityFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7708-9ef7-55330e63b20b" xlink:to="loc_alx_PropertyManagementCleaningEngineeringParkingAndSecurityFeesMember_01a03a2a-ad40-7f01-8f7d-e79e9a5088b0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisAxis_01a03a2a-ad40-74fc-b16f-ca21d896348a" xlink:href="alx-20260930.xsd#alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-795f-aa6b-f74d2c30ced3" xlink:to="loc_alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisAxis_01a03a2a-ad40-74fc-b16f-ca21d896348a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisDomain_01a03a2a-ad40-74fc-b16f-ca21d896348a_default" xlink:href="alx-20260930.xsd#alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisAxis_01a03a2a-ad40-74fc-b16f-ca21d896348a" xlink:to="loc_alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisDomain_01a03a2a-ad40-74fc-b16f-ca21d896348a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisDomain_01a03a2a-ad40-7cb0-8e32-cd975787b77b" xlink:href="alx-20260930.xsd#alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisAxis_01a03a2a-ad40-74fc-b16f-ca21d896348a" xlink:to="loc_alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisDomain_01a03a2a-ad40-7cb0-8e32-cd975787b77b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RegoParkIPropertyMember_01a03a2a-ad40-7aac-932d-179d8dd98590" xlink:href="alx-20260930.xsd#alx_RegoParkIPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxisDomain_01a03a2a-ad40-7cb0-8e32-cd975787b77b" xlink:to="loc_alx_RegoParkIPropertyMember_01a03a2a-ad40-7aac-932d-179d8dd98590" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_01a03a2a-ad40-7a96-8875-a61e4a5ba548" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_01a03a2a-ad40-7a96-8875-a61e4a5ba548" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ManagementFeeAgreementValue_01a03a2a-ad40-78c9-b3d5-849ce7f45a65" xlink:href="alx-20260930.xsd#alx_ManagementFeeAgreementValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_alx_ManagementFeeAgreementValue_01a03a2a-ad40-78c9-b3d5-849ce7f45a65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyManagementFeePercentFee_01a03a2a-ad40-72b2-b2e1-10e77cf93015" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyManagementFeePercentFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_us-gaap_PropertyManagementFeePercentFee_01a03a2a-ad40-72b2-b2e1-10e77cf93015" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PropertyManagementFeeAgreementPricePerSquareFoot_01a03a2a-ad40-731d-896b-4d01d4d80004" xlink:href="alx-20260930.xsd#alx_PropertyManagementFeeAgreementPricePerSquareFoot"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_alx_PropertyManagementFeeAgreementPricePerSquareFoot_01a03a2a-ad40-731d-896b-4d01d4d80004" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_01a03a2a-ad40-7617-9289-077ce0855997" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_01a03a2a-ad40-7617-9289-077ce0855997" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PropertyManagementFeeEscalationPercentagePerAnnum_01a03a2a-ad40-7793-99ab-ff8af7b7f28d" xlink:href="alx-20260930.xsd#alx_PropertyManagementFeeEscalationPercentagePerAnnum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_alx_PropertyManagementFeeEscalationPercentagePerAnnum_01a03a2a-ad40-7793-99ab-ff8af7b7f28d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DevelopmentFeePercentage_01a03a2a-ad40-7e0e-8de5-c75c7353279b" xlink:href="alx-20260930.xsd#alx_DevelopmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_alx_DevelopmentFeePercentage_01a03a2a-ad40-7e0e-8de5-c75c7353279b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LeaseFeePercentageOfRentOneToTenYears_01a03a2a-ad40-75de-86a8-45350ed8c6f0" xlink:href="alx-20260930.xsd#alx_LeaseFeePercentageOfRentOneToTenYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_alx_LeaseFeePercentageOfRentOneToTenYears_01a03a2a-ad40-75de-86a8-45350ed8c6f0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LeaseFeePercentageOfRentElevenToTwentyYears_01a03a2a-ad40-799b-a5f9-6395bfaee71b" xlink:href="alx-20260930.xsd#alx_LeaseFeePercentageOfRentElevenToTwentyYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_alx_LeaseFeePercentageOfRentElevenToTwentyYears_01a03a2a-ad40-799b-a5f9-6395bfaee71b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LeaseFeePercentageOfRentTwentyFirstToThirtyYears_01a03a2a-ad40-7c66-ba65-5e6906c8b589" xlink:href="alx-20260930.xsd#alx_LeaseFeePercentageOfRentTwentyFirstToThirtyYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_alx_LeaseFeePercentageOfRentTwentyFirstToThirtyYears_01a03a2a-ad40-7c66-ba65-5e6906c8b589" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LeaseCommissionPercentage_01a03a2a-ad40-7c0d-88b6-9bb81f20a1f0" xlink:href="alx-20260930.xsd#alx_LeaseCommissionPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_alx_LeaseCommissionPercentage_01a03a2a-ad40-7c0d-88b6-9bb81f20a1f0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PercentageCommissionsOnSaleOfAssetsUnderFiftyMillion_01a03a2a-ad40-77e9-bb2a-9c7c2a9d0949" xlink:href="alx-20260930.xsd#alx_PercentageCommissionsOnSaleOfAssetsUnderFiftyMillion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_alx_PercentageCommissionsOnSaleOfAssetsUnderFiftyMillion_01a03a2a-ad40-77e9-bb2a-9c7c2a9d0949" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_AssetSaleCommissionThreshold_01a03a2a-ad40-7500-a12a-1664244da01a" xlink:href="alx-20260930.xsd#alx_AssetSaleCommissionThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_alx_AssetSaleCommissionThreshold_01a03a2a-ad40-7500-a12a-1664244da01a" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PercentageCommissionsOnSaleOfAssetsOverFiftyMillion_01a03a2a-ad40-7cca-be08-71377f1bbe57" xlink:href="alx-20260930.xsd#alx_PercentageCommissionsOnSaleOfAssetsOverFiftyMillion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_alx_PercentageCommissionsOnSaleOfAssetsOverFiftyMillion_01a03a2a-ad40-7cca-be08-71377f1bbe57" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForCommissions_01a03a2a-ad40-70cb-8296-993b8e04ec95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForCommissions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_us-gaap_PaymentsForCommissions_01a03a2a-ad40-70cb-8296-993b8e04ec95" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilities_01a03a2a-ad40-736a-a4b0-7b483c15f183" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-7064-ba2e-8875c7be73b2" xlink:to="loc_us-gaap_OtherLiabilities_01a03a2a-ad40-736a-a4b0-7b483c15f183" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/RelatedPartyTransactionsScheduleofFeestoVornadoDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#RelatedPartyTransactionsScheduleofFeestoVornadoDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/RelatedPartyTransactionsScheduleofFeestoVornadoDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-72d8-b310-13b3685a9110" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-7c52-9e0d-994357e35e98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-72d8-b310-13b3685a9110" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-7c52-9e0d-994357e35e98" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_01a03a2a-ad40-7d18-b668-d69ba0046d01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a03a2a-ad40-7c52-9e0d-994357e35e98" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_01a03a2a-ad40-7d18-b668-d69ba0046d01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7d18-b668-d69ba0046d01_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_01a03a2a-ad40-7d18-b668-d69ba0046d01" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7d18-b668-d69ba0046d01_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7151-8448-e0e78002426a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_01a03a2a-ad40-7d18-b668-d69ba0046d01" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7151-8448-e0e78002426a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_CompanyManagementFeesMember_01a03a2a-ad40-7826-9c06-71653d9987a6" xlink:href="alx-20260930.xsd#alx_CompanyManagementFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7151-8448-e0e78002426a" xlink:to="loc_alx_CompanyManagementFeesMember_01a03a2a-ad40-7826-9c06-71653d9987a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DevelopmentFeesMember_01a03a2a-ad40-763b-bd1c-0e2baf87ecaf" xlink:href="alx-20260930.xsd#alx_DevelopmentFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7151-8448-e0e78002426a" xlink:to="loc_alx_DevelopmentFeesMember_01a03a2a-ad40-763b-bd1c-0e2baf87ecaf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LeasingFeesMember_01a03a2a-ad40-7576-844b-0d9fc70606d1" xlink:href="alx-20260930.xsd#alx_LeasingFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7151-8448-e0e78002426a" xlink:to="loc_alx_LeasingFeesMember_01a03a2a-ad40-7576-844b-0d9fc70606d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_CommissionOnSaleOfRealEstateMember_01a03a2a-ad40-7d9f-8b4d-91f72ff05ef1" xlink:href="alx-20260930.xsd#alx_CommissionOnSaleOfRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7151-8448-e0e78002426a" xlink:to="loc_alx_CommissionOnSaleOfRealEstateMember_01a03a2a-ad40-7d9f-8b4d-91f72ff05ef1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_PropertyManagementCleaningEngineeringParkingAndSecurityFeesMember_01a03a2a-ad40-77ed-835d-e951d1e69286" xlink:href="alx-20260930.xsd#alx_PropertyManagementCleaningEngineeringParkingAndSecurityFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_01a03a2a-ad40-7151-8448-e0e78002426a" xlink:to="loc_alx_PropertyManagementCleaningEngineeringParkingAndSecurityFeesMember_01a03a2a-ad40-77ed-835d-e951d1e69286" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_01a03a2a-ad40-7c2f-82d5-76fd1a63d495" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a03a2a-ad40-72d8-b310-13b3685a9110" xlink:to="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_01a03a2a-ad40-7c2f-82d5-76fd1a63d495" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/MortgagesPayableScheduleofOutstandingMortgagesPayableDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#MortgagesPayableScheduleofOutstandingMortgagesPayableDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/MortgagesPayableScheduleofOutstandingMortgagesPayableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7eef-9217-cf347e72ea36" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-74e0-aa03-8a0b871f9254" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateScheduleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7eef-9217-cf347e72ea36" xlink:to="loc_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-74e0-aa03-8a0b871f9254" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a03a2a-ad40-7df2-882f-594a10077f3b" 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_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-74e0-aa03-8a0b871f9254" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a03a2a-ad40-7df2-882f-594a10077f3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-7df2-882f-594a10077f3b_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_01a03a2a-ad40-7df2-882f-594a10077f3b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-7df2-882f-594a10077f3b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-7702-91c1-878faca4a3f5" 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_01a03a2a-ad40-7df2-882f-594a10077f3b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-7702-91c1-878faca4a3f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgagesMember_01a03a2a-ad40-7495-af36-e39b903070de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgagesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-7702-91c1-878faca4a3f5" xlink:to="loc_us-gaap_MortgagesMember_01a03a2a-ad40-7495-af36-e39b903070de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7c31-9ddd-16e1cd5cee73" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-74e0-aa03-8a0b871f9254" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7c31-9ddd-16e1cd5cee73" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-7c31-9ddd-16e1cd5cee73_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7c31-9ddd-16e1cd5cee73" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-7c31-9ddd-16e1cd5cee73_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-719b-91f8-01e3179dab66" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-7c31-9ddd-16e1cd5cee73" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-719b-91f8-01e3179dab66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LexingtonAvenuePropertyMember_01a03a2a-ad40-7cbd-94a1-28890186cac0" xlink:href="alx-20260930.xsd#alx_LexingtonAvenuePropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-719b-91f8-01e3179dab66" xlink:to="loc_alx_LexingtonAvenuePropertyMember_01a03a2a-ad40-7cbd-94a1-28890186cac0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RegoParkShoppingCenterMember_01a03a2a-ad40-7948-8eab-d5f1d1b532a5" xlink:href="alx-20260930.xsd#alx_RegoParkShoppingCenterMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-719b-91f8-01e3179dab66" xlink:to="loc_alx_RegoParkShoppingCenterMember_01a03a2a-ad40-7948-8eab-d5f1d1b532a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_AlexanderApartmentTowerMember_01a03a2a-ad40-754a-8539-5822331122f7" xlink:href="alx-20260930.xsd#alx_AlexanderApartmentTowerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-719b-91f8-01e3179dab66" xlink:to="loc_alx_AlexanderApartmentTowerMember_01a03a2a-ad40-754a-8539-5822331122f7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-74ea-ba78-bcdda9163c0b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-74e0-aa03-8a0b871f9254" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-74ea-ba78-bcdda9163c0b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-74ea-ba78-bcdda9163c0b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-74ea-ba78-bcdda9163c0b" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-74ea-ba78-bcdda9163c0b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7232-8029-90076d8f6ee3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-74ea-ba78-bcdda9163c0b" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7232-8029-90076d8f6ee3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OfficeBuildingMember_01a03a2a-ad40-71db-a93d-40884863ee21" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OfficeBuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7232-8029-90076d8f6ee3" xlink:to="loc_srt_OfficeBuildingMember_01a03a2a-ad40-71db-a93d-40884863ee21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RetailSiteMember_01a03a2a-ad40-7fa5-9b85-e9bc1d2c4478" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RetailSiteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7232-8029-90076d8f6ee3" xlink:to="loc_srt_RetailSiteMember_01a03a2a-ad40-7fa5-9b85-e9bc1d2c4478" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ApartmentBuildingMember_01a197db-5793-7784-af4e-f2c66f608485" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ApartmentBuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7232-8029-90076d8f6ee3" xlink:to="loc_srt_ApartmentBuildingMember_01a197db-5793-7784-af4e-f2c66f608485" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a03a2a-ad40-7ae6-b47f-a3e4bdf837de" 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_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-74e0-aa03-8a0b871f9254" xlink:to="loc_srt_RangeAxis_01a03a2a-ad40-7ae6-b47f-a3e4bdf837de" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03a2a-ad40-7ae6-b47f-a3e4bdf837de_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_01a03a2a-ad40-7ae6-b47f-a3e4bdf837de" xlink:to="loc_srt_RangeMember_01a03a2a-ad40-7ae6-b47f-a3e4bdf837de_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03a2a-ad40-7e6c-99e8-774673ec523b" 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_01a03a2a-ad40-7ae6-b47f-a3e4bdf837de" xlink:to="loc_srt_RangeMember_01a03a2a-ad40-7e6c-99e8-774673ec523b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a03a2a-ad40-7e0b-8ad2-bc12fd55a898" 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_01a03a2a-ad40-7e6c-99e8-774673ec523b" xlink:to="loc_srt_MaximumMember_01a03a2a-ad40-7e0b-8ad2-bc12fd55a898" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a03a2a-ad40-78d9-ac9e-9d87d9e3fd04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7eef-9217-cf347e72ea36" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a03a2a-ad40-78d9-ac9e-9d87d9e3fd04" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_NotesPayableGross_01a03a2a-ad40-778b-bdb0-c6748c2b9a0a" xlink:href="alx-20260930.xsd#alx_NotesPayableGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7eef-9217-cf347e72ea36" xlink:to="loc_alx_NotesPayableGross_01a03a2a-ad40-778b-bdb0-c6748c2b9a0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_01a03a2a-ad40-760b-9d46-6e6c8a8ab4da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7eef-9217-cf347e72ea36" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_01a03a2a-ad40-760b-9d46-6e6c8a8ab4da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayable_01a03a2a-ad40-7865-8756-8b7a8d642ac7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7eef-9217-cf347e72ea36" xlink:to="loc_us-gaap_NotesPayable_01a03a2a-ad40-7865-8756-8b7a8d642ac7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_01a03a2a-ad40-7308-8833-89927d19221a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedAmortizationDeferredFinanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7eef-9217-cf347e72ea36" xlink:to="loc_us-gaap_AccumulatedAmortizationDeferredFinanceCosts_01a03a2a-ad40-7308-8833-89927d19221a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_01a03a2a-ad40-779e-a9c3-40fee3033660" 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_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7eef-9217-cf347e72ea36" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_01a03a2a-ad40-779e-a9c3-40fee3033660" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaidInKindInterest_01a03a2a-ad40-7b7c-ad35-0ef22ddf12d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaidInKindInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7eef-9217-cf347e72ea36" xlink:to="loc_us-gaap_PaidInKindInterest_01a03a2a-ad40-7b7c-ad35-0ef22ddf12d1" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/MortgagesPayableNarrativeDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#MortgagesPayableNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/MortgagesPayableNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7e8b-bc19-ca0de6022db9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-7c58-be4f-9aed31f793ef" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateScheduleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7e8b-bc19-ca0de6022db9" xlink:to="loc_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-7c58-be4f-9aed31f793ef" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-7204-9b0e-7af09e79aa2c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-7c58-be4f-9aed31f793ef" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-7204-9b0e-7af09e79aa2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7204-9b0e-7af09e79aa2c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-7204-9b0e-7af09e79aa2c" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-7204-9b0e-7af09e79aa2c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-70b0-b557-0b4868f3bcb6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_01a03a2a-ad40-7204-9b0e-7af09e79aa2c" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-70b0-b557-0b4868f3bcb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RetailSiteMember_01a03a2a-ad40-7d18-a31e-a2a8b8bca88d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RetailSiteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_01a03a2a-ad40-70b0-b557-0b4868f3bcb6" xlink:to="loc_srt_RetailSiteMember_01a03a2a-ad40-7d18-a31e-a2a8b8bca88d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-71ef-aa08-fcf4ba8a4304" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-7c58-be4f-9aed31f793ef" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-71ef-aa08-fcf4ba8a4304" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-71ef-aa08-fcf4ba8a4304_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-71ef-aa08-fcf4ba8a4304" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-71ef-aa08-fcf4ba8a4304_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-78ab-811f-1b08f231e020" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_01a03a2a-ad40-71ef-aa08-fcf4ba8a4304" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-78ab-811f-1b08f231e020" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LexingtonAvenuePropertyMember_01a03a2a-ad40-7a00-9671-cf072083c510" xlink:href="alx-20260930.xsd#alx_LexingtonAvenuePropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_01a03a2a-ad40-78ab-811f-1b08f231e020" xlink:to="loc_alx_LexingtonAvenuePropertyMember_01a03a2a-ad40-7a00-9671-cf072083c510" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a03a2a-ad40-7a0f-9443-258fe5178353" 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_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-7c58-be4f-9aed31f793ef" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a03a2a-ad40-7a0f-9443-258fe5178353" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-7a0f-9443-258fe5178353_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_01a03a2a-ad40-7a0f-9443-258fe5178353" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-7a0f-9443-258fe5178353_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-71cf-9830-045ccf8df26b" 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_01a03a2a-ad40-7a0f-9443-258fe5178353" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-71cf-9830-045ccf8df26b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgagesMember_01a03a2a-ad40-7479-b755-d6f24d1b44e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgagesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-71cf-9830-045ccf8df26b" xlink:to="loc_us-gaap_MortgagesMember_01a03a2a-ad40-7479-b755-d6f24d1b44e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_01a03a2a-ad40-74f4-8800-1ef6775d7a7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-71cf-9830-045ccf8df26b" xlink:to="loc_us-gaap_SeniorNotesMember_01a03a2a-ad40-74f4-8800-1ef6775d7a7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_JuniorSubordinatedDebtMember_01a03a2a-ad40-74f1-870b-547a28f0c2a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_JuniorSubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-71cf-9830-045ccf8df26b" xlink:to="loc_us-gaap_JuniorSubordinatedDebtMember_01a03a2a-ad40-74f1-870b-547a28f0c2a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorSubordinatedNotesMember_01a03a2a-ad40-7a48-85f7-e56c442cde6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorSubordinatedNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a03a2a-ad40-71cf-9830-045ccf8df26b" xlink:to="loc_us-gaap_SeniorSubordinatedNotesMember_01a03a2a-ad40-7a48-85f7-e56c442cde6d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DebtCovenantAxisAxis_01a03a2a-ad40-7e27-8ad2-3b81ff47f287" xlink:href="alx-20260930.xsd#alx_DebtCovenantAxisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-7c58-be4f-9aed31f793ef" xlink:to="loc_alx_DebtCovenantAxisAxis_01a03a2a-ad40-7e27-8ad2-3b81ff47f287" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DebtCovenantAxisDomain_01a03a2a-ad40-7e27-8ad2-3b81ff47f287_default" xlink:href="alx-20260930.xsd#alx_DebtCovenantAxisDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_alx_DebtCovenantAxisAxis_01a03a2a-ad40-7e27-8ad2-3b81ff47f287" xlink:to="loc_alx_DebtCovenantAxisDomain_01a03a2a-ad40-7e27-8ad2-3b81ff47f287_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DebtCovenantAxisDomain_01a03a2a-ad40-7fcd-a333-04ceb6664613" xlink:href="alx-20260930.xsd#alx_DebtCovenantAxisDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_alx_DebtCovenantAxisAxis_01a03a2a-ad40-7e27-8ad2-3b81ff47f287" xlink:to="loc_alx_DebtCovenantAxisDomain_01a03a2a-ad40-7fcd-a333-04ceb6664613" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LoanAmountsBelow65MMember_01a03a2a-ad40-7dbe-9afe-4edbb7dcf625" xlink:href="alx-20260930.xsd#alx_LoanAmountsBelow65MMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_DebtCovenantAxisDomain_01a03a2a-ad40-7fcd-a333-04ceb6664613" xlink:to="loc_alx_LoanAmountsBelow65MMember_01a03a2a-ad40-7dbe-9afe-4edbb7dcf625" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_LoanAmountsAbove65MMember_01a03a2a-ad40-7f0f-832c-e6916a1d7957" xlink:href="alx-20260930.xsd#alx_LoanAmountsAbove65MMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_DebtCovenantAxisDomain_01a03a2a-ad40-7fcd-a333-04ceb6664613" xlink:to="loc_alx_LoanAmountsAbove65MMember_01a03a2a-ad40-7f0f-832c-e6916a1d7957" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a03a2a-ad40-7e68-8709-e758874279b2" 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_srt_MortgageLoansOnRealEstateScheduleTable_01a03a2a-ad40-7c58-be4f-9aed31f793ef" xlink:to="loc_srt_RangeAxis_01a03a2a-ad40-7e68-8709-e758874279b2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03a2a-ad40-7e68-8709-e758874279b2_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_01a03a2a-ad40-7e68-8709-e758874279b2" xlink:to="loc_srt_RangeMember_01a03a2a-ad40-7e68-8709-e758874279b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a03a2a-ad40-7ed6-b1d5-103fa72adb9f" 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_01a03a2a-ad40-7e68-8709-e758874279b2" xlink:to="loc_srt_RangeMember_01a03a2a-ad40-7ed6-b1d5-103fa72adb9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a03a2a-ad40-7337-ac4c-a6345f0deebe" 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_01a03a2a-ad40-7ed6-b1d5-103fa72adb9f" xlink:to="loc_srt_MinimumMember_01a03a2a-ad40-7337-ac4c-a6345f0deebe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_01a03a2a-ad40-7cfe-919c-8c42d9384367" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7e8b-bc19-ca0de6022db9" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_01a03a2a-ad40-7cfe-919c-8c42d9384367" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a03a2a-ad40-7fec-956b-5f8886718c78" 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_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7e8b-bc19-ca0de6022db9" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a03a2a-ad40-7fec-956b-5f8886718c78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_01a03a2a-ad40-779d-9cff-e4b023310244" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateLineItems_01a03a2a-ad40-7e8b-bc19-ca0de6022db9" xlink:to="loc_us-gaap_LongTermDebt_01a03a2a-ad40-779d-9cff-e4b023310244" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/StockBasedCompensationDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#StockBasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/StockBasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03a2a-ad40-79fb-8746-f8560d6edd3d" 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_01a03a2a-ad40-73e1-968e-9730d46ab396" 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_01a03a2a-ad40-79fb-8746-f8560d6edd3d" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a03a2a-ad40-73e1-968e-9730d46ab396" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_01a03a2a-ad40-7c56-bc0a-26fd5a68015e" 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_01a03a2a-ad40-73e1-968e-9730d46ab396" xlink:to="loc_us-gaap_PlanNameAxis_01a03a2a-ad40-7c56-bc0a-26fd5a68015e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a03a2a-ad40-7c56-bc0a-26fd5a68015e_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_01a03a2a-ad40-7c56-bc0a-26fd5a68015e" xlink:to="loc_us-gaap_PlanNameDomain_01a03a2a-ad40-7c56-bc0a-26fd5a68015e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a03a2a-ad40-776b-bb76-744f0c8b448e" 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_01a03a2a-ad40-7c56-bc0a-26fd5a68015e" xlink:to="loc_us-gaap_PlanNameDomain_01a03a2a-ad40-776b-bb76-744f0c8b448e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_A2026OmnibusStockPlanMember_01a03a2a-ad40-7dcd-bc0b-883961ee108c" xlink:href="alx-20260930.xsd#alx_A2026OmnibusStockPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_01a03a2a-ad40-776b-bb76-744f0c8b448e" xlink:to="loc_alx_A2026OmnibusStockPlanMember_01a03a2a-ad40-7dcd-bc0b-883961ee108c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_01a03a2a-ad40-7d63-b2eb-c5ef9a2e92cc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a03a2a-ad40-73e1-968e-9730d46ab396" xlink:to="loc_srt_TitleOfIndividualAxis_01a03a2a-ad40-7d63-b2eb-c5ef9a2e92cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a03a2a-ad40-7d63-b2eb-c5ef9a2e92cc_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_01a03a2a-ad40-7d63-b2eb-c5ef9a2e92cc" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a03a2a-ad40-7d63-b2eb-c5ef9a2e92cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a03a2a-ad40-74cf-907c-9a4a7e096745" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_01a03a2a-ad40-7d63-b2eb-c5ef9a2e92cc" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a03a2a-ad40-74cf-907c-9a4a7e096745" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_DirectorMember_01a03a2a-ad40-7aaa-92ad-a49bcf0b304d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_DirectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a03a2a-ad40-74cf-907c-9a4a7e096745" xlink:to="loc_srt_DirectorMember_01a03a2a-ad40-7aaa-92ad-a49bcf0b304d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a03a2a-ad40-75f6-bd04-feb4584d1cdd" 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_01a03a2a-ad40-73e1-968e-9730d46ab396" xlink:to="loc_us-gaap_AwardTypeAxis_01a03a2a-ad40-75f6-bd04-feb4584d1cdd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03a2a-ad40-75f6-bd04-feb4584d1cdd_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_01a03a2a-ad40-75f6-bd04-feb4584d1cdd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03a2a-ad40-75f6-bd04-feb4584d1cdd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03a2a-ad40-7f7e-8d40-2a8e3e1e6fcf" 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_01a03a2a-ad40-75f6-bd04-feb4584d1cdd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03a2a-ad40-7f7e-8d40-2a8e3e1e6fcf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_DeferredStockUnitsMember_01a03a2a-ad40-732b-8123-ce43e2b9298b" xlink:href="alx-20260930.xsd#alx_DeferredStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a03a2a-ad40-7f7e-8d40-2a8e3e1e6fcf" xlink:to="loc_alx_DeferredStockUnitsMember_01a03a2a-ad40-732b-8123-ce43e2b9298b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedPerDirector_01a03a2a-ad40-72f3-a8fe-4ed12b705ea3" xlink:href="alx-20260930.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedPerDirector"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03a2a-ad40-79fb-8746-f8560d6edd3d" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedPerDirector_01a03a2a-ad40-72f3-a8fe-4ed12b705ea3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsMarketValue_01a03a2a-ad40-72d4-857c-d0a1e7c84fc4" xlink:href="alx-20260930.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsMarketValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03a2a-ad40-79fb-8746-f8560d6edd3d" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsMarketValue_01a03a2a-ad40-72d4-857c-d0a1e7c84fc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValuePerGrant_01a03a2a-ad40-70ff-9f27-73485f1dd3e1" xlink:href="alx-20260930.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValuePerGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03a2a-ad40-79fb-8746-f8560d6edd3d" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValuePerGrant_01a03a2a-ad40-70ff-9f27-73485f1dd3e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValueTotal_01a03a2a-ad40-7971-93eb-4c46d9a53fef" xlink:href="alx-20260930.xsd#alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValueTotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03a2a-ad40-79fb-8746-f8560d6edd3d" xlink:to="loc_alx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantDateFairValueTotal_01a03a2a-ad40-7971-93eb-4c46d9a53fef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_01a03a2a-ad40-7f78-a8d5-a93d8210dd75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03a2a-ad40-79fb-8746-f8560d6edd3d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_01a03a2a-ad40-7f78-a8d5-a93d8210dd75" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_01a03a2a-ad40-71b1-b502-39304099c8c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a03a2a-ad40-79fb-8746-f8560d6edd3d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_01a03a2a-ad40-71b1-b502-39304099c8c7" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/FairValueMeasurementsScheduleofFinancialAssetsMeasuredatFairValueDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#FairValueMeasurementsScheduleofFinancialAssetsMeasuredatFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/FairValueMeasurementsScheduleofFinancialAssetsMeasuredatFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03a2a-ad40-7113-be2e-91e248abffdd" 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_01a03a2a-ad40-7da4-a629-3efd45b8a036" 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_01a03a2a-ad40-7113-be2e-91e248abffdd" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03a2a-ad40-7da4-a629-3efd45b8a036" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a03a2a-ad40-7dbd-adc7-cfdd63f0d792" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03a2a-ad40-7da4-a629-3efd45b8a036" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a03a2a-ad40-7dbd-adc7-cfdd63f0d792" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03a2a-ad40-7dbd-adc7-cfdd63f0d792_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_01a03a2a-ad40-7dbd-adc7-cfdd63f0d792" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03a2a-ad40-7dbd-adc7-cfdd63f0d792_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03a2a-ad40-7cc5-ac49-a221f1ccad82" 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_01a03a2a-ad40-7dbd-adc7-cfdd63f0d792" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03a2a-ad40-7cc5-ac49-a221f1ccad82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_01a03a2a-ad40-7c55-833c-c74ef586a448" 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_01a03a2a-ad40-7cc5-ac49-a221f1ccad82" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_01a03a2a-ad40-7c55-833c-c74ef586a448" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_01a03a2a-ad40-75e9-b057-101643428737" 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_01a03a2a-ad40-7cc5-ac49-a221f1ccad82" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_01a03a2a-ad40-75e9-b057-101643428737" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_01a03a2a-ad40-7501-8596-fe360b876872" 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_01a03a2a-ad40-7cc5-ac49-a221f1ccad82" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_01a03a2a-ad40-7501-8596-fe360b876872" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateDerivativeAssetsAtFairValue_01a03a2a-ad40-70d1-a10d-c1b9ec6003c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateDerivativeAssetsAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03a2a-ad40-7113-be2e-91e248abffdd" xlink:to="loc_us-gaap_InterestRateDerivativeAssetsAtFairValue_01a03a2a-ad40-70d1-a10d-c1b9ec6003c6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/FairValueMeasurementsScheduleofInterestRateDerivativesDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#FairValueMeasurementsScheduleofInterestRateDerivativesDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/FairValueMeasurementsScheduleofInterestRateDerivativesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03a2a-ad40-7985-8014-94315b38fa7c" 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_01a03a2a-ad40-723e-b5ae-4e580475ddeb" 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_01a03a2a-ad40-7985-8014-94315b38fa7c" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03a2a-ad40-723e-b5ae-4e580475ddeb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03a2a-ad40-76cd-8baf-063417f478bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03a2a-ad40-723e-b5ae-4e580475ddeb" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03a2a-ad40-76cd-8baf-063417f478bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a03a2a-ad40-76cd-8baf-063417f478bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03a2a-ad40-76cd-8baf-063417f478bd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a03a2a-ad40-76cd-8baf-063417f478bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a03a2a-ad40-72ee-939a-085bd2d6df59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a03a2a-ad40-76cd-8baf-063417f478bd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a03a2a-ad40-72ee-939a-085bd2d6df59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_01a03a2a-ad40-7cf9-aeff-08e1928e1547" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a03a2a-ad40-72ee-939a-085bd2d6df59" xlink:to="loc_us-gaap_InterestRateSwapMember_01a03a2a-ad40-7cf9-aeff-08e1928e1547" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_01a03a2a-ad40-7622-8b62-2a691c0d7b1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03a2a-ad40-723e-b5ae-4e580475ddeb" xlink:to="loc_us-gaap_HedgingDesignationAxis_01a03a2a-ad40-7622-8b62-2a691c0d7b1f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a03a2a-ad40-7622-8b62-2a691c0d7b1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a03a2a-ad40-7622-8b62-2a691c0d7b1f" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a03a2a-ad40-7622-8b62-2a691c0d7b1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a03a2a-ad40-7031-9af1-dd9b4a7dc790" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a03a2a-ad40-7622-8b62-2a691c0d7b1f" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a03a2a-ad40-7031-9af1-dd9b4a7dc790" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_01a03a2a-ad40-7d8f-b34d-c354d713b2e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_01a03a2a-ad40-7031-9af1-dd9b4a7dc790" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_01a03a2a-ad40-7d8f-b34d-c354d713b2e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a03a2a-ad40-76d7-b235-3be8e6404928" 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_01a03a2a-ad40-723e-b5ae-4e580475ddeb" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a03a2a-ad40-76d7-b235-3be8e6404928" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a03a2a-ad40-76d7-b235-3be8e6404928_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_01a03a2a-ad40-76d7-b235-3be8e6404928" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a03a2a-ad40-76d7-b235-3be8e6404928_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a03a2a-ad40-7ec0-8652-9f3fe3603297" 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_01a03a2a-ad40-76d7-b235-3be8e6404928" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a03a2a-ad40-7ec0-8652-9f3fe3603297" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RegoParkShoppingCenterMortgageLoanMember_01a03a2a-ad40-7def-8b86-ab8ba765ef15" xlink:href="alx-20260930.xsd#alx_RegoParkShoppingCenterMortgageLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a03a2a-ad40-7ec0-8652-9f3fe3603297" xlink:to="loc_alx_RegoParkShoppingCenterMortgageLoanMember_01a03a2a-ad40-7def-8b86-ab8ba765ef15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_01a03a2a-ad40-72d3-a1db-bba20fc2a051" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03a2a-ad40-7985-8014-94315b38fa7c" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_01a03a2a-ad40-72d3-a1db-bba20fc2a051" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetNotionalAmount_01a03a2a-ad40-71ad-a5bc-c202ca7773c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03a2a-ad40-7985-8014-94315b38fa7c" xlink:to="loc_us-gaap_DerivativeAssetNotionalAmount_01a03a2a-ad40-71ad-a5bc-c202ca7773c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCapInterestRate_01a03a2a-ad40-7b80-8b9d-0f77f8af38b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeCapInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03a2a-ad40-7985-8014-94315b38fa7c" xlink:to="loc_us-gaap_DerivativeCapInterestRate_01a03a2a-ad40-7b80-8b9d-0f77f8af38b8" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/FairValueMeasurementsScheduleofCarryingAmountandFairValueofFinancialInstrumentsDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#FairValueMeasurementsScheduleofCarryingAmountandFairValueofFinancialInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/FairValueMeasurementsScheduleofCarryingAmountandFairValueofFinancialInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03a2a-ad40-71d9-85f9-db52df20b3bd" 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_01a03a2a-ad40-7838-9fa5-511f76519686" 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_01a03a2a-ad40-71d9-85f9-db52df20b3bd" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03a2a-ad40-7838-9fa5-511f76519686" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a03a2a-ad40-7abc-8b6b-d3e59c42a6e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a03a2a-ad40-7838-9fa5-511f76519686" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a03a2a-ad40-7abc-8b6b-d3e59c42a6e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03a2a-ad40-7abc-8b6b-d3e59c42a6e2_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_01a03a2a-ad40-7abc-8b6b-d3e59c42a6e2" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03a2a-ad40-7abc-8b6b-d3e59c42a6e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03a2a-ad40-79f9-abcf-e299e6d7ad63" 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_01a03a2a-ad40-7abc-8b6b-d3e59c42a6e2" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a03a2a-ad40-79f9-abcf-e299e6d7ad63" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_01a03a2a-ad40-76a9-a9e6-d04e9940510d" 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_01a03a2a-ad40-79f9-abcf-e299e6d7ad63" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_01a03a2a-ad40-76a9-a9e6-d04e9940510d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_01a03a2a-ad40-7c21-824e-7022563f7cac" 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_01a03a2a-ad40-79f9-abcf-e299e6d7ad63" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_01a03a2a-ad40-7c21-824e-7022563f7cac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_01a03a2a-ad40-7979-9a1b-11acde257a83" 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_01a03a2a-ad40-7838-9fa5-511f76519686" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_01a03a2a-ad40-7979-9a1b-11acde257a83" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a03a2a-ad40-7979-9a1b-11acde257a83_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_01a03a2a-ad40-7979-9a1b-11acde257a83" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a03a2a-ad40-7979-9a1b-11acde257a83_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a03a2a-ad40-7640-9e43-2db97524c981" 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_01a03a2a-ad40-7979-9a1b-11acde257a83" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a03a2a-ad40-7640-9e43-2db97524c981" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a03a2a-ad40-7e7e-84a0-9948e65a2ea3" 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_01a03a2a-ad40-7640-9e43-2db97524c981" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a03a2a-ad40-7e7e-84a0-9948e65a2ea3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_01a03a2a-ad40-7d90-ab12-d3b44d636662" 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_01a03a2a-ad40-7e7e-84a0-9948e65a2ea3" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_01a03a2a-ad40-7d90-ab12-d3b44d636662" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a03a2a-ad40-78fa-82d1-c5decb3485e0" 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_01a03a2a-ad40-7e7e-84a0-9948e65a2ea3" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a03a2a-ad40-78fa-82d1-c5decb3485e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7d05-a081-0114e2167807" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03a2a-ad40-71d9-85f9-db52df20b3bd" xlink:to="loc_us-gaap_AssetsAbstract_01a03a2a-ad40-7d05-a081-0114e2167807" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_01a03a2a-ad40-77bf-b5ed-374152e33f4a" 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_AssetsAbstract_01a03a2a-ad40-7d05-a081-0114e2167807" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_01a03a2a-ad40-77bf-b5ed-374152e33f4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_01a03a2a-ad40-76e1-bdb1-cf594da06273" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a03a2a-ad40-71d9-85f9-db52df20b3bd" xlink:to="loc_us-gaap_LiabilitiesAbstract_01a03a2a-ad40-76e1-bdb1-cf594da06273" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableFairValueDisclosure_01a03a2a-ad40-73f2-b6da-67e187839e36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_01a03a2a-ad40-76e1-bdb1-cf594da06273" xlink:to="loc_us-gaap_NotesPayableFairValueDisclosure_01a03a2a-ad40-73f2-b6da-67e187839e36" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/CommitmentsandContingenciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_01a03a2a-ad40-71e5-a58c-8eecfc1542df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_01a03a2a-ad40-7a3e-b69f-07865989a339" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_01a03a2a-ad40-71e5-a58c-8eecfc1542df" xlink:to="loc_us-gaap_LossContingenciesTable_01a03a2a-ad40-7a3e-b69f-07865989a339" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_01a03a2a-ad40-7861-a8e7-3bef158729fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_01a03a2a-ad40-7a3e-b69f-07865989a339" xlink:to="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_01a03a2a-ad40-7861-a8e7-3bef158729fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeAndTierIdentifierDomain_01a03a2a-ad40-7861-a8e7-3bef158729fc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeAndTierIdentifierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_01a03a2a-ad40-7861-a8e7-3bef158729fc" xlink:to="loc_us-gaap_TypeAndTierIdentifierDomain_01a03a2a-ad40-7861-a8e7-3bef158729fc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeAndTierIdentifierDomain_01a03a2a-ad40-7185-86d0-aa124d5d0aac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeAndTierIdentifierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ScheduleOfMalpracticeInsuranceTypeAndTierIdentifierAxis_01a03a2a-ad40-7861-a8e7-3bef158729fc" xlink:to="loc_us-gaap_TypeAndTierIdentifierDomain_01a03a2a-ad40-7185-86d0-aa124d5d0aac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralLiabilityMember_01a03a2a-ad40-7f61-b6a4-efc42f11474b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralLiabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeAndTierIdentifierDomain_01a03a2a-ad40-7185-86d0-aa124d5d0aac" xlink:to="loc_us-gaap_GeneralLiabilityMember_01a03a2a-ad40-7f61-b6a4-efc42f11474b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_01a03a2a-ad40-7a3f-b96f-8613ee96d72b" xlink:href="alx-20260930.xsd#alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_01a03a2a-ad40-7a3e-b69f-07865989a339" xlink:to="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_01a03a2a-ad40-7a3f-b96f-8613ee96d72b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierDomain_01a03a2a-ad40-7a3f-b96f-8613ee96d72b_default" xlink:href="alx-20260930.xsd#alx_ScheduleOfInsuranceTypeAndTierIdentifierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_01a03a2a-ad40-7a3f-b96f-8613ee96d72b" xlink:to="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierDomain_01a03a2a-ad40-7a3f-b96f-8613ee96d72b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierDomain_01a03a2a-ad40-74f8-a817-e4617e66e146" xlink:href="alx-20260930.xsd#alx_ScheduleOfInsuranceTypeAndTierIdentifierDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis_01a03a2a-ad40-7a3f-b96f-8613ee96d72b" xlink:to="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierDomain_01a03a2a-ad40-74f8-a817-e4617e66e146" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_AllRiskPropertyAndRentalValueMember_01a03a2a-ad40-7170-95ea-c17e0f9d7f41" xlink:href="alx-20260930.xsd#alx_AllRiskPropertyAndRentalValueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierDomain_01a03a2a-ad40-74f8-a817-e4617e66e146" xlink:to="loc_alx_AllRiskPropertyAndRentalValueMember_01a03a2a-ad40-7170-95ea-c17e0f9d7f41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_TerrorismCoverageIncludingNbcrMember_01a03a2a-ad40-7842-88c3-b51a8796c5a1" xlink:href="alx-20260930.xsd#alx_TerrorismCoverageIncludingNbcrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierDomain_01a03a2a-ad40-74f8-a817-e4617e66e146" xlink:to="loc_alx_TerrorismCoverageIncludingNbcrMember_01a03a2a-ad40-7842-88c3-b51a8796c5a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_NbcrMember_01a03a2a-ad40-7ab3-89eb-f195e47d1e57" xlink:href="alx-20260930.xsd#alx_NbcrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_ScheduleOfInsuranceTypeAndTierIdentifierDomain_01a03a2a-ad40-74f8-a817-e4617e66e146" xlink:to="loc_alx_NbcrMember_01a03a2a-ad40-7ab3-89eb-f195e47d1e57" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a03a2a-ad40-7bf7-b8ef-6b5121df7156" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_01a03a2a-ad40-7a3e-b69f-07865989a339" xlink:to="loc_dei_LegalEntityAxis_01a03a2a-ad40-7bf7-b8ef-6b5121df7156" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a03a2a-ad40-7bf7-b8ef-6b5121df7156_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a03a2a-ad40-7bf7-b8ef-6b5121df7156" xlink:to="loc_dei_EntityDomain_01a03a2a-ad40-7bf7-b8ef-6b5121df7156_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a03a2a-ad40-74ec-b827-d34bc87fe4f4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a03a2a-ad40-7bf7-b8ef-6b5121df7156" xlink:to="loc_dei_EntityDomain_01a03a2a-ad40-74ec-b827-d34bc87fe4f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_FiftyNinthStreetInsuranceCompanyLlcMember_01a03a2a-ad40-7d65-9fc3-5f5e3d354b45" xlink:href="alx-20260930.xsd#alx_FiftyNinthStreetInsuranceCompanyLlcMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a03a2a-ad40-74ec-b827-d34bc87fe4f4" xlink:to="loc_alx_FiftyNinthStreetInsuranceCompanyLlcMember_01a03a2a-ad40-7d65-9fc3-5f5e3d354b45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstatePropertyOccupantAxis_01a151d7-28cf-7d0b-9feb-d8828a156db3" xlink:href="alx-20260930.xsd#alx_RealEstatePropertyOccupantAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_01a03a2a-ad40-7a3e-b69f-07865989a339" xlink:to="loc_alx_RealEstatePropertyOccupantAxis_01a151d7-28cf-7d0b-9feb-d8828a156db3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstatePropertyOccupantDomain_01a151d7-28cf-7d0b-9feb-d8828a156db3_default" xlink:href="alx-20260930.xsd#alx_RealEstatePropertyOccupantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_alx_RealEstatePropertyOccupantAxis_01a151d7-28cf-7d0b-9feb-d8828a156db3" xlink:to="loc_alx_RealEstatePropertyOccupantDomain_01a151d7-28cf-7d0b-9feb-d8828a156db3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_RealEstatePropertyOccupantDomain_01a151d7-28cf-714e-b994-279af1b66aa8" xlink:href="alx-20260930.xsd#alx_RealEstatePropertyOccupantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_alx_RealEstatePropertyOccupantAxis_01a151d7-28cf-7d0b-9feb-d8828a156db3" xlink:to="loc_alx_RealEstatePropertyOccupantDomain_01a151d7-28cf-714e-b994-279af1b66aa8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_FlushingPropertyMember_01a151d7-9a95-745a-a82c-52d13b71883d" xlink:href="alx-20260930.xsd#alx_FlushingPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alx_RealEstatePropertyOccupantDomain_01a151d7-28cf-714e-b994-279af1b66aa8" xlink:to="loc_alx_FlushingPropertyMember_01a151d7-9a95-745a-a82c-52d13b71883d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_01a1785b-27fa-7214-8d5e-bb7b8dd5be27" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_01a03a2a-ad40-7a3e-b69f-07865989a339" xlink:to="loc_srt_StatementScenarioAxis_01a1785b-27fa-7214-8d5e-bb7b8dd5be27" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_01a1785b-27fa-7214-8d5e-bb7b8dd5be27_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_01a1785b-27fa-7214-8d5e-bb7b8dd5be27" xlink:to="loc_srt_ScenarioUnspecifiedDomain_01a1785b-27fa-7214-8d5e-bb7b8dd5be27_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_01a1785b-27fa-73bd-a91b-99a33f99012b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_01a1785b-27fa-7214-8d5e-bb7b8dd5be27" xlink:to="loc_srt_ScenarioUnspecifiedDomain_01a1785b-27fa-73bd-a91b-99a33f99012b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_01a1785b-3b96-7335-8a80-22bd180d32f4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_01a1785b-27fa-73bd-a91b-99a33f99012b" xlink:to="loc_srt_ScenarioForecastMember_01a1785b-3b96-7335-8a80-22bd180d32f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a1804e-1d41-74a0-9fa7-d7512c30a1fe" 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_LossContingenciesTable_01a03a2a-ad40-7a3e-b69f-07865989a339" xlink:to="loc_srt_RangeAxis_01a1804e-1d41-74a0-9fa7-d7512c30a1fe" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1804e-1d41-74a0-9fa7-d7512c30a1fe_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_01a1804e-1d41-74a0-9fa7-d7512c30a1fe" xlink:to="loc_srt_RangeMember_01a1804e-1d41-74a0-9fa7-d7512c30a1fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1804e-1d41-781c-8e1b-ff7cf12f7b51" 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_01a1804e-1d41-74a0-9fa7-d7512c30a1fe" xlink:to="loc_srt_RangeMember_01a1804e-1d41-781c-8e1b-ff7cf12f7b51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a1804e-8e40-70cf-98ba-0a9dd7883d3d" 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_01a1804e-1d41-781c-8e1b-ff7cf12f7b51" xlink:to="loc_srt_MinimumMember_01a1804e-8e40-70cf-98ba-0a9dd7883d3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a1804e-d574-78bc-9e69-58c361cd871c" 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_01a1804e-1d41-781c-8e1b-ff7cf12f7b51" xlink:to="loc_srt_MaximumMember_01a1804e-d574-78bc-9e69-58c361cd871c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_InsuranceMaximumCoveragePerProperty_01a03a2a-ad40-7726-aaea-574d7a033c7b" xlink:href="alx-20260930.xsd#alx_InsuranceMaximumCoveragePerProperty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_01a03a2a-ad40-71e5-a58c-8eecfc1542df" xlink:to="loc_alx_InsuranceMaximumCoveragePerProperty_01a03a2a-ad40-7726-aaea-574d7a033c7b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_InsuranceMaximumCoveragePerIncident_01a03a2a-ad40-7065-abdb-21b508b6d0d0" xlink:href="alx-20260930.xsd#alx_InsuranceMaximumCoveragePerIncident"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_01a03a2a-ad40-71e5-a58c-8eecfc1542df" xlink:to="loc_alx_InsuranceMaximumCoveragePerIncident_01a03a2a-ad40-7065-abdb-21b508b6d0d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_InsuranceMaximumCoverageInAggregate_01a03a2a-ad40-7a9d-87e4-607f569306e7" xlink:href="alx-20260930.xsd#alx_InsuranceMaximumCoverageInAggregate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_01a03a2a-ad40-71e5-a58c-8eecfc1542df" xlink:to="loc_alx_InsuranceMaximumCoverageInAggregate_01a03a2a-ad40-7a9d-87e4-607f569306e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_InsuranceDeductible_01a03a2a-ad40-7a20-8e01-84f2315af730" xlink:href="alx-20260930.xsd#alx_InsuranceDeductible"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_01a03a2a-ad40-71e5-a58c-8eecfc1542df" xlink:to="loc_alx_InsuranceDeductible_01a03a2a-ad40-7a20-8e01-84f2315af730" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_SelfInsuredResponsibility_01a03a2a-ad40-70b9-af64-2a162d40fce9" xlink:href="alx-20260930.xsd#alx_SelfInsuredResponsibility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_01a03a2a-ad40-71e5-a58c-8eecfc1542df" xlink:to="loc_alx_SelfInsuredResponsibility_01a03a2a-ad40-70b9-af64-2a162d40fce9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_FederalGovernmentResponsibility_01a03a2a-ad40-781b-af75-26172369b8d1" xlink:href="alx-20260930.xsd#alx_FederalGovernmentResponsibility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_01a03a2a-ad40-71e5-a58c-8eecfc1542df" xlink:to="loc_alx_FederalGovernmentResponsibility_01a03a2a-ad40-781b-af75-26172369b8d1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_01a1785a-72bc-768f-9dc2-a9a62524648d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_01a03a2a-ad40-71e5-a58c-8eecfc1542df" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_01a1785a-72bc-768f-9dc2-a9a62524648d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceived_01a1785d-b41b-77b6-9de1-af65959774fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_01a03a2a-ad40-71e5-a58c-8eecfc1542df" xlink:to="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceived_01a1785d-b41b-77b6-9de1-af65959774fd" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/SegmentInformationScheduleofSummaryofNOIDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#SegmentInformationScheduleofSummaryofNOIDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/SegmentInformationScheduleofSummaryofNOIDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-7c52-af58-30a985a52998" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03a2a-ad40-72b9-974f-dfeb778d4e70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-7c52-af58-30a985a52998" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03a2a-ad40-72b9-974f-dfeb778d4e70" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a03a2a-ad40-708d-bb1f-c5afdedfbe0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03a2a-ad40-72b9-974f-dfeb778d4e70" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a03a2a-ad40-708d-bb1f-c5afdedfbe0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03a2a-ad40-708d-bb1f-c5afdedfbe0e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03a2a-ad40-708d-bb1f-c5afdedfbe0e" xlink:to="loc_us-gaap_SegmentDomain_01a03a2a-ad40-708d-bb1f-c5afdedfbe0e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03a2a-ad40-71e5-a0ac-f858bd2affce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03a2a-ad40-708d-bb1f-c5afdedfbe0e" xlink:to="loc_us-gaap_SegmentDomain_01a03a2a-ad40-71e5-a0ac-f858bd2affce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ReportableSegmentMember_01a03a2a-ad40-7e2d-8e72-18cee3013b24" xlink:href="alx-20260930.xsd#alx_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03a2a-ad40-71e5-a0ac-f858bd2affce" xlink:to="loc_alx_ReportableSegmentMember_01a03a2a-ad40-7e2d-8e72-18cee3013b24" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_01a03a2a-ad40-7913-b1b5-adc620607d5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-7c52-af58-30a985a52998" xlink:to="loc_us-gaap_Revenues_01a03a2a-ad40-7913-b1b5-adc620607d5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateTaxExpense_01a03a2a-ad40-78e7-b1b0-d8f0cc718d51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateTaxExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-7c52-af58-30a985a52998" xlink:to="loc_us-gaap_RealEstateTaxExpense_01a03a2a-ad40-78e7-b1b0-d8f0cc718d51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_01a03a2a-ad40-7c98-9c02-3b4946a3012e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-7c52-af58-30a985a52998" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_01a03a2a-ad40-7c98-9c02-3b4946a3012e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpenses_01a03a2a-ad40-7833-a3b6-c803aabe0afa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingCostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-7c52-af58-30a985a52998" xlink:to="loc_us-gaap_OperatingCostsAndExpenses_01a03a2a-ad40-7833-a3b6-c803aabe0afa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_01a03a2a-ad40-706b-abb9-1f033d055d7d" 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_SegmentReportingInformationLineItems_01a03a2a-ad40-7c52-af58-30a985a52998" xlink:to="loc_us-gaap_OperatingIncomeLoss_01a03a2a-ad40-706b-abb9-1f033d055d7d" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alx-inc.com/role/SegmentInformationScheduleNOItoNetIncomeDetails" xlink:type="simple" xlink:href="alx-20260930.xsd#SegmentInformationScheduleNOItoNetIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.alx-inc.com/role/SegmentInformationScheduleNOItoNetIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-723e-87a7-7e5b9afc3f95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03a2a-ad40-7698-adc4-908891e6125c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-723e-87a7-7e5b9afc3f95" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03a2a-ad40-7698-adc4-908891e6125c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a03a2a-ad40-79b9-ae54-27a253048bad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a03a2a-ad40-7698-adc4-908891e6125c" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a03a2a-ad40-79b9-ae54-27a253048bad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03a2a-ad40-79b9-ae54-27a253048bad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03a2a-ad40-79b9-ae54-27a253048bad" xlink:to="loc_us-gaap_SegmentDomain_01a03a2a-ad40-79b9-ae54-27a253048bad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a03a2a-ad40-7a66-a6f2-0aac7c3e8485" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a03a2a-ad40-79b9-ae54-27a253048bad" xlink:to="loc_us-gaap_SegmentDomain_01a03a2a-ad40-7a66-a6f2-0aac7c3e8485" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_ReportableSegmentMember_01a03a2a-ad40-74b1-835d-22a0857a6650" xlink:href="alx-20260930.xsd#alx_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a03a2a-ad40-7a66-a6f2-0aac7c3e8485" xlink:to="loc_alx_ReportableSegmentMember_01a03a2a-ad40-74b1-835d-22a0857a6650" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_01a03a2a-ad40-76c7-be05-3927039863f4" 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_SegmentReportingInformationLineItems_01a03a2a-ad40-723e-87a7-7e5b9afc3f95" xlink:to="loc_us-gaap_OperatingIncomeLoss_01a03a2a-ad40-76c7-be05-3927039863f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDebtExpense_01a03a2a-ad40-7672-b72a-f10e10f53a4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDebtExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-723e-87a7-7e5b9afc3f95" xlink:to="loc_us-gaap_InterestAndDebtExpense_01a03a2a-ad40-7672-b72a-f10e10f53a4f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndOtherIncome_01a03a2a-ad40-7f04-aa8a-18b4f411d7ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndOtherIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-723e-87a7-7e5b9afc3f95" xlink:to="loc_us-gaap_InterestAndOtherIncome_01a03a2a-ad40-7f04-aa8a-18b4f411d7ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_01a03a2a-ad40-7f6d-a90b-ae12e80f2d64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-723e-87a7-7e5b9afc3f95" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_01a03a2a-ad40-7f6d-a90b-ae12e80f2d64" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_01a03a2a-ad40-741a-9188-cd6a09a6b71c" 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_SegmentReportingInformationLineItems_01a03a2a-ad40-723e-87a7-7e5b9afc3f95" xlink:to="loc_us-gaap_DepreciationAndAmortization_01a03a2a-ad40-741a-9188-cd6a09a6b71c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alx_GainsLossesOnSalesOfInvestmentRealEstateIncludingDiscontinuedOperations_01a03a2a-ad40-749c-af50-6b64b71c104e" xlink:href="alx-20260930.xsd#alx_GainsLossesOnSalesOfInvestmentRealEstateIncludingDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-723e-87a7-7e5b9afc3f95" xlink:to="loc_alx_GainsLossesOnSalesOfInvestmentRealEstateIncludingDiscontinuedOperations_01a03a2a-ad40-749c-af50-6b64b71c104e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a03a2a-ad40-73b8-9721-a346df628df2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a03a2a-ad40-723e-87a7-7e5b9afc3f95" xlink:to="loc_us-gaap_NetIncomeLoss_01a03a2a-ad40-73b8-9721-a346df628df2" xlink:type="arc" order="6"/>
  </link:definitionLink>
</link:linkbase>
