knuckle under

verb

1. intr, adverb to give way under pressure or authority; yield

Idioms and Phrases

Also, knuckle down . Give in, acknowledge defeat, as in The dean refused to knuckle under to the graduate students' demands , or He was forced to knuckle down before their threats of violence . Presumably this idiom alludes to a kneeling position with hands on the ground, knuckles down. [Mid-1700s]