mutter
definition: a complaint uttered in a low and indistinct tone
example:
speech part: noun
synonyms:
grumbling
definition: a low continuous indistinct sound
example:
speech part: noun
synonyms:
murmuring
definition: make complaining remarks or noises under one's breath
example:
speech part: verb
synonyms:
murmur
definition: talk indistinctly
example:
speech part: verb
synonyms:
mumble