From Longman Dictionary of Contemporary Englishgentleman's agreementˌgentleman’s aˈgreement noun [countable] AGREEan agreement that is not written down, made between people who trust each other
Examples from the Corpus
gentleman's agreement• Such is our gentleman's agreement.From Longman Business Dictionarygentleman's agreementˈgentleman's aˌgreement an informal agreement that is not written down, made between people who trust and respect each otherIt suited both parties for their arrangements to be by gentleman’s agreement. → agreement 