say something, speak, mutter, etc. under your breathidiomPart ofbreathsay something, speak, mutter, etc. under your breathsay something, speak, mutter, etc. under your breath — idiomidiom1. To say something very quietly so that other people cannot hear it.1.idiomDefinitionTo say something very quietly so that other people cannot hear it.ExampleWhen the boss made the announcement, Tom muttered a complaint under his breath.She spoke an insult under her breath, hoping no one would hear.