Mumble/ˈmʌmbl/ Definition 1 of 2Pro Tip 1/3Informal Context Use 'mumble' for casual or informal situations, not in formal communication. Talking to his friends, he mumbled the details of his weekend plans. Pro Tip 2/3Unclear Speech 'Mumble' suggests the speaker is not enunciating clearly, often on purpose or out of habit. He always mumbles his name so I never learn it. Pro Tip 3/3Lack of Confidence Mumbling can reflect a lack of confidence or discomfort in speaking. Nervous, she mumbled her presentation to the class.