Noun

• S: (n) mutter, muttering, murmur, murmuring, murmuration, mussitation (a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech)
• S: (n) grumble, grumbling, murmur, murmuring, mutter, muttering (a complaint uttered in a low and indistinct tone)
• direct hypernym / inherited hypernym / sister term
• S: (n) complaint (an expression of grievance or resentment)
• S: (n) objection (the speech act of objecting)
• S: (n) speech act (the use of language to perform some act)
• S: (n) act, deed, human action, human activity (something that people do or cause to happen)
• S: (n) event (something that happens at a given place and time)
• S: (n) psychological feature (a feature of the mental life of a living organism)
• S: (n) abstraction, abstract entity (a general concept formed by extracting common features from specific examples)
• S: (n) entity (that which is perceived or known or inferred to have its own distinct existence (living or nonliving))
• derivationally related form

Verb

• S: (v) murmur (speak softly or indistinctly) "She murmured softly to the baby in her arms"
• S: (v) murmur, mutter, grumble, croak, gnarl (make complaining remarks or noises under one's breath) "she grumbles when she feels overworked"

Adjective

• S: (adj) murmuring, susurrant, whispering (making a low continuous indistinct sound) "like murmuring waves"; "susurrant voices"