knuckle under

Example: “The small suppliers had to knuckle under to the chain's demands.”

Origin: Grew out of the 18th-century "knuckle down" and the standalone verb "knuckle," both already meaning to submit or acknowledge defeat by that period — Dyche and Pardon's 1740 dictionary defines "knuckle" alone as "to stoop, bend, yield, comply with, or submit to." One theory ties this submissive sense to an older use of "knuckle" for the knee rather than the hand, making the gesture behind the idiom closer to kneeling than to any hand position at all. A separate, unverified story instead points to the custom of rapping one's knuckles against the underside of a table as a physical signal of conceding an argument. "Knuckle under" specifically, an American coinage using the same core word with a different preposition, is first documented in print in 1882, and the exact reason the newer form displaced or supplemented the older "knuckle down" isn't clearly recorded.