under (one's) breath(redirected from under their breaths)
under (one's) breath
Spoken in such a soft, quiet voice that others cannot hear it distinctly. "You'll get what's coming to you one of these days," Janet muttered under her breath.
*under one's breath
Fig. [spoken] so softly that almost no one can hear it. (*Typically: curse ~; curse some-one or something ~; mutter ~; mutter something ~; say something ~.) John was muttering something under his breath, and I don't think it was very pleasant. I'm glad he said it under his breath. If he had said it out loud, it would have caused an argument.
under one's breath
Softly, in an undertone or whisper, as in "I can't stand one more minute of that music," she muttered under her breath. This idiom, first recorded in 1832, is probably a hyperbole, alluding to a sound that is softer than breathing.