knuckling under

Verb

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.
   • The man is a ruffian. I won't knuckle under to him!1907, John Galsworthy, “Acute Attack of—‘Pendycitis’”, in The Country House, London: William Heinemann, →OCLC, part III, page 286

   Synonyms:

   fall in line