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. (intransitive, idiomatic) To yield or cooperate when pressured or forced to do so.
   • 1907, John Galsworthy, chapter 8, in The Country House:

     "Nothing shall induce me!" he said. . . . "The man is a ruffian. I won't knuckle under to him!"

• fall in line

• “knuckle under”, in OneLook Dictionary Search.