bygones n. + Add to list US //ˈbaɪˌɡɔnz// UK //bˈaɪɡɒnz// by·gones SynonymsEtymology Synonyms bygoneOrigin Plural of bygone (noun). Idioms1 entry01let bygones be bygonesTo disregard or ignore a past difficulty in a relationship or an offence (when dealing with another individual).