noun · hesitant or afraid to speak out or criticize someone because of received favors or personal obligation

吃人家的嘴软，拿了礼物的他现在不敢再提反对意见了。

verb · softening one's tone or backing down from a stubborn position; no longer speaking firmly or defiantly

在确凿的证据面前，原本嘴硬的他终于嘴软了。