mutter

mut-ter

verb

To speak in a low, indistinct voice, often expressing dissatisfaction or annoyance.

"He began to mutter about the delay."

noun

A low, indistinct sound or utterance, often expressing complaint or discontent.

"There was a low mutter from the crowd."

Thesaurus

Synonyms: maunder, mussitate, mumble, murmuring, murmur, murmuration, mussitation, muttering, croak, grumble, gnarl, grumbling