<p><strong>Verb</strong></p><ul><li>(used without object) to utter words indistinctly or in a low tone, often as if talking to oneself; murmur.</li><li>to complain murmuringly; grumble.</li><li>to make a low, rumbling sound.</li></ul><p><strong>Noun</strong></p><ul><li>the act or utterance of a person who mutters.</li></ul>