let bygones be bygones

From bygone (“event that happened in the past”).

• (Received Pronunciation) IPA^(key): /lɛt ˈbaɪɡɒnz biː ˈbaɪɡɒnz/

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• (General American) IPA^(key): /lɛt ˈbaɪˌɡɑnz bi ˈbaɪˌɡɑnz/
• Hyphenation: let by‧gones be by‧gones

let bygones be bygones (third-person singular simple present lets bygones be bygones, present participle letting bygones be bygones, simple past and past participle let bygones be bygones)

1. (intransitive, idiomatic) To disregard or ignore a past difficulty in a relationship or an offence (when dealing with another individual).

   Synonym: forgive and forget

   • 1881, P. Chr. Asbjörnsen [i.e., Peter Christen Asbjørnsen], “Peik”, in H. L. Brækstad, transl., Round the Yule Log. Norwegian Folk and Fairy Tales, London: Sampson Low, Marston, Searle, & Rivington, →OCLC, page 196:

     "Never mind, I'll give you a hundred dollars for it," said the king; "you did me out of horse and saddle the other day, and the bridle too, but I'll let bygones be bygones, if I get the pot."

   • 1886 May, Thomas Hardy, chapter 44, in The Life and Death of the Mayor of Casterbridge: The Story of a Man of Character, London: The Folio Society, published 1968 (1996 printing), →OCLC, page 323:

     To intrude as little of his personality as possible upon a gay event with which that personality could show nothing in keeping, he decided not to make his appearance till evening—when stiffness would have worn off, and a gentle wish to let bygones be bygones would exercise its say in all hearts.

   • 1958, Elizabeth George Speare, chapter 20, in The Witch of Blackbird Pond, Boston, Mass.: Houghton Mifflin Company, published 1986, →ISBN, pages 228–229:

     You'll find, when you come back, I promise you, Kit, that everyone is willing to let bygones be bygones, and that you can make a fresh start.

   • 1992, Ethel Footman Smothers, “Let Bygones Be Bygones”, in Down in the Piney Woods (A Borzoi Book), New York, N.Y.: Alfred A[braham] Knopf, →ISBN, page 145:

     But I ain't got no quarrel witcha. Just let bygones be bygones.

• let sleeping dogs lie
• water under the bridge

• “bygones are bygones, let bygones be bygones, etc.” under “bygone, adj. and n.”, in OED Online ⁠, Oxford, Oxfordshire: Oxford University Press, September 2022.
• “let bygones be bygones, phrase”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.