Definition of the word knuckle under

The phrase "knuckle under" is a slang expression that originated in the mid-20th century. It describes the action of surrendering or yielding, often after being subjected to pressure or force. The term's origin is attributed to the act of a person, particularly a fighter or boxer, relenting and lowering their guard by bringing their knuckles, or fists, down in submission. The idiomatic expression "knuckle under" is a metaphorical interpretation of this action, where the gesture of lowering fists implies a reluctant surrender or concession. In fact, the Oxford English Dictionary traces the expression back to the 1940s, noting its usage in Hollywood films as part of slang-laden dialogue in boxing movies. The exact origins of the term, however, remain somewhat unclear, as alternative theories suggest it may stem from the practice of soldiers "performing knucklepush-ups" or lowering themselves in a military formation as a sign of submission during training exercises. Regardless of its root, "knuckle under" remains a colloquial and vivid way of describing the act of relenting or surrendering in modern-day English.