say (something) under (one's) breath
To mutter something in such a soft, quiet voice that others cannot hear it distinctly, especially rude, unpleasant, complaining, or impertinent remarks. I could hear Bill saying something under his breath on the way back to his desk after his annual review. Don't you dare say such vile words under your breath at me, young lady!
Farlex Dictionary of Idioms. © 2024 Farlex, Inc, all rights reserved.