"Knuckling under" is an idiomatic expression that refers to yielding or giving in to someone or something. There are many synonyms for this phrase, including submitting, surrendering, capitulating, acquiescing, complying, obeying, conforming, relenting, succumbing, and bowing down. Each of these words describes a different aspect of the act of yielding, but all convey the same general idea. The use of this expression can vary depending on the context and the tone of the conversation. While some may view "knuckling under" as a sign of weakness, others may see it as a necessary compromise or a gesture of respect.