a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech

同义词：muttering  /  murmur  /  murmuring  /  murmuration  /  mussitation

a complaint uttered in a low and indistinct tone

同义词：grumble  /  grumbling  /  murmur  /  murmuring  /  muttering

talk indistinctly; usually in a low voice

同义词：mumble  /  maunder  /  mussitate

make complaining remarks or noises under one's breath

同义词：murmur  /  grumble  /  croak  /  gnarl