Under one’s breath is an idiom that originated in the United States. We will examine the meaning of the common saying under one’s breath, where it came from, and some examples of its idiomatic usage in sentences.
To say something under one’s breath means to speak softly or in a barely audible whisper so that others cannot clearly hear what one has said. People often mutter under their breaths when cursing or complaining or saying something that they don’t quite want someone else to hear. The expression under one’s breath came into use in the 1830s, presumably to mean something that is said more softly than the sound of breathing.
Kings guard De’Aaron Fox said Ingles will make humorous comments under his breath here and there, but it’s normally not anything that gets under the skin. (Deseret News)
Under his breath he muttered a curse–a minor curse, not one of the big ones–and walked back to his office, his morning ruined. (Arkansas Democrat-Gazette)
“I was with the Queen, but my husband was with him and said he kept making remarks about the proceedings under his breath as they went on,” Mrs. Lodge told the News-Press on Friday. (Santa Barbara News-Press)