At a loss for words is a phrase used to describe someone who is unable to think of the right words to say in a particular situation. The crossword solutions for this phrase are HUM (3 letters), HUMS (4 letters), and TONGUETIED (10 letters). HUM is an informal verb meaning to make a low, continuous sound, usually to express emotion. HUMS is the third person singular present form of the verb, and TONGUETIED is an adjective meaning unable to speak due to being overwhelmed or embarrassed.