Gentlemen's agreement

understanding between two people that is based on their word of honor

verbal agreement or deal, agreement bound by honor rather than law

A Gentlemen's agreement is an informal agreement between two or more parties. It may be written or oral. The essence of a gentleman's agreement is that it relies upon the honor of the parties for its fulfilment, rather than being in any way enforceable. It is, therefore, distinct from a legal agreement or contract, which can be enforced if necessary. The phrase's first recorded use was in 1888 in the Report of the Railway Accounting Officers published by the Association of American Railroads Accounting Division (page 337).
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Noun
1. a personal agreement based on honor and not legally binding
(hypernym) agreement, understanding