1. (v. i.) To utter words indistinctly or with a low voice and lips partly closed; esp., to utter indistinct complaints or angry expressions; to grumble; to growl.

2. (v. i.) To sound with a low, rumbling noise.

3. (v. t.) To utter with imperfect articulations, or with a low voice; as, to mutter threats.

4. (n.) Repressed or obscure utterance.

air a grievance aspirate aspiration bark bated breath bawl beef bellow bellyache bitch blare blat blubber boom bray breath breathe breathy voice buzz cackle chant chirp clamor complain coo crab croak crow cry dolorous tirade drawl drone droning exclaim exhalation flute fret fret and fume fumble fuss gabble gasp gibber gibbering gripe groan grouch grouse growl grumble grunt hiss holler howl jabber jeremiad jibber keen kick lament lilt little voice lodge a complaint low voice maffle maunder maundering moan mouth mouthing muddle mumble mumbling murmur murmuration murmuring mussitate muttering outcry pant pipe plaint planctus raise a howl register a complaint repine roar rumble rumor scold scream screech shriek sibilate sigh sing snap snarl snort sob soft voice sough speak incoherently splutter sputter squall squawk squeal stage whisper still small voice susurrate susurration susurrus swallow take on thunder tirade trumpet twang ululation underbreath undertone wail wail of woe warble whimper whine whisper whispering whistle yap yawp yell yelp yowl