Mutter (verb)

Speak softly and indistinctly, especially in a low voice and with a discontented or angry tone.

Origin:

Middle english: from middle low german muttern.

Examples:

1. She was muttering to herself about the traffic.
2. He muttered an expletive under his breath.
3. The old man was muttering about the cold weather.
4. She muttered a prayer before starting her presentation.
5. The teacher asked the student to stop muttering and pay attention.