Knuckle under is an idiom that means to accept defeat or SUBMIT to someone else's authority. The crossword solutions for this term include DEFER (5 letters), CAPITULATE (10 letters), BOW (3 letters), SUBMIT (6 letters), YIELD (5 letters), ACCEDE (6 letters), SUCCUMB (7 letters), CAVE (4 letters), GIVE (4 letters), OBEY (4 letters), bowto (5 letters), givein (6 letters), abideby (7 letters), and yieldtopressure (15 letters). All of these words imply a sense of surrendering or giving in to someone else's demands.