WordWeb Online

1. A low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech
   - mutter, murmur, murmuring, murmuration, mussitation
    
2. A complaint uttered in a low and indistinct tone
   - grumble, grumbling, murmur, murmuring, mutter

1. Talk indistinctly; usually in a low voice
   - mumble, maunder, mussitate
    
2. Make complaining remarks or noises under one's breath
   "she mutters when she feels overworked";
   - murmur, grumble, croak, gnarl [archaic], chunter [Brit, informal]

Derived forms: mutterings

Type of: complain, complaint, kick [informal], kvetch [N. Amer, informal], moan, mouth, plain [archaic], sound, sound off, speak, talk, utter, verbalise [Brit], verbalize

Encyclopedia: Mutter, Stefan