knuckle under

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knuckle under (third-person singular simple present knuckles under, present participle knuckling under, simple past and past participle knuckled under)

1. (idiomatic, intransitive) To cooperate or yield when forced or pressured to do so.

   Synonym: fall in line

   • 1907, John Galsworthy, “Acute Attack of—‘Pendycitis’”, in The Country House, London: William Heinemann, →OCLC, part III, page 286:

     The man is a ruffian. I won't knuckle under to him!

• “knuckle under”, in OneLook Dictionary Search.