murmur

(noun) a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech. Synonyms: mutter, muttering, murmuring, murmuration, mussitation.

(noun) a schwa that is incidental to the pronunciation of a consonant. Synonyms: murmur vowel.

(noun) an abnormal sound of the heart; sometimes a sign of abnormal function of the heart valves. Synonyms: heart murmur, cardiac murmur.

(noun) a complaint uttered in a low and indistinct tone. Synonyms: grumble, grumbling, murmuring, mutter, muttering.

(verb) speak softly or indistinctly. Examples: "She murmured softly to the baby in her arms."

(verb) make complaining remarks or noises under one's breath. Synonyms: mutter, grumble, croak, gnarl. Examples: "She grumbles when she feels overworked."