English to English

noun (n)

• a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech(noun.event)

  Synonym:
  murmur, murmuration, murmuring, mussitation, mutter
  

  source: wordnet30
• a complaint uttered in a low and indistinct tone(noun.communication)

  Synonym:
  grumble, grumbling, murmur, murmuring, mutter
  

  source: wordnet30