Under one’s breath

Under one’s breath is an idiom that originated in the United States. An idiom is a commonly used word, group of words, or phrase that has a figurative meaning that is not easily deduced from its literal definition. Often using descriptive imagery or metaphors, common idioms are words and phrases used in the English language in […]
from Grammarist
https://grammarist.com/idiom/under-ones-breath/