Complain Under One's Breath is an expression used to describe a situation in which someone expresses their dissatisfaction or displeasure in a quiet, subtle way. The two crossword solutions for this term are MUTTER (6 letters) and GRUMBLE (7 letters). MUTTER is defined as speaking quietly and indistinctly, while GRUMBLE is defined as expressing discontent or dissatisfaction in a low, sullen voice. Both words can be used to describe the act of Complaining Under One's Breath.