mutter (something) under (one's) breath(redirected from mutter under their breath)
mutter (something) under (one's) breath
To murmur something in such a soft, quiet voice that others cannot hear it distinctly. (Said especially of rude, unpleasant, complaining, or impertinent remarks.) I could hear Bill muttering something under his breath on the way back to his desk after his annual review. Don't you dare mutter curse words under your breath at me, young lady!