murmur in WordNet English dictionary

1. an abnormal sound of the heart; sometimes a sign of abnormal function of the heart valves
   heart murmur  cardiac murmur  murmur 
   
2. a complaint uttered in a low and indistinct tone
   grumble  grumbling  murmur  murmuring  mutter  muttering 
   
3. a schwa that is incidental to the pronunciation of a consonant
   murmur vowel  murmur 
   
4. a low continuous indistinct sound; often accompanied by movement of the lips without the production of articulate speech
   mutter  muttering  murmur  murmuring  murmuration  mussitation 
   

1. make complaining remarks or noises under one's breath
   "she grumbles when she feels overworked"
   murmur  mutter  grumble  croak  gnarl 
   
2. speak softly or indistinctly
   "She murmured softly to the baby in her arms"
   murmur