intransitive verb
Definition: To speak quietly and unclearly, often in a way that is hard to understand, usually because of annoyance or dissatisfaction.
Example: She began to mutter under her breath when she heard the news.
noun
Definition: A quiet or soft sound made when someone speaks in a low voice, often difficult to hear clearly.
Example: I could hear his mutter as he complained about the weather.
transitive verb
Definition: To speak or say something quietly and unclearly, often in a way that is difficult to hear.
Example: She began to mutter under her breath when she was frustrated.