underbreath adjective 1adverb 1noun 1forms 3 adjective1 •Vocalized under one's breath.Aleck gave a low, underbreath whistle. — 1886 adverb1 •Under one's breath; inaudibly or in a barely audible manner.Muttering curses underbreath, he jabs the beast sharply with his training stick ; the elephant is hairy and it, like the clown, is ignoble. — 1978 noun1 •An utterance made so as not to be heard by most people in the area.The underbreath of our every prayer should be, “Father, not my will, but thine be done” — 1845 formsunderbreaths · more underbreath · most underbreath