The Collaborative International Dictionary of English v.0.48:

Murmur \Mur"mur\, n. [F. murmure: cf. L. murmur. CF. Murmur,
   v. i.]
   1. A low, confused, and indistinct sound, like that of
      running water.
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   2. A complaint half suppressed, or uttered in a low,
      muttering voice. --Chaucer.
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            Some discontents there are, some idle murmurs.
                                                  --Dryden.
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The Collaborative International Dictionary of English v.0.48:

Murmur \Mur"mur\, v. i. [imp. & p. p. Murmured; p. pr. & vb.
   n. Murmuring.] [F. murmurer, L. murmurare, murmurari, fr.
   murmur murmur; cf. Gr. ? to roar and boil, said of water,
   Skr. marmara a rustling sound; prob. of imitative origin.]
   1. To make a low continued noise, like the hum of bees, a
      stream of water, distant waves, or the wind in a forest.
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            They murmured as doth a swarm of bees. --Chaucer.
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   2. To utter complaints in a low, half-articulated voice; to
      feel or express dissatisfaction or discontent; to grumble;
      -- often with at or against. "His disciples murmured at
      it." --John vi. 61.
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            And all the children of Israel murmured against
            Moses and against Aaron.              --Num. xiv. 2.
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            Neither murmur ye, as some of them also murmured.
                                                  --1 Cor. x.
                                                  10.
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The Collaborative International Dictionary of English v.0.48:

Murmur \Mur"mur\, v. t.
   To utter or give forth in low or indistinct words or sounds;
   as, to murmur tales. --Shak.
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         The people murmured such things concerning him. --John
                                                  vii. 32.
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WordNet (r) 3.0 (2006):

murmur
    n 1: a low continuous indistinct sound; often accompanied by
         movement of the lips without the production of articulate
         speech [syn: mutter, muttering, murmur, murmuring,
         murmuration, mussitation]
    2: a schwa that is incidental to the pronunciation of a
       consonant [syn: murmur vowel, murmur]
    3: an abnormal sound of the heart; sometimes a sign of abnormal
       function of the heart valves [syn: heart murmur, cardiac
       murmur, murmur]
    4: a complaint uttered in a low and indistinct tone [syn:
       grumble, grumbling, murmur, murmuring, mutter,
       muttering]
    v 1: speak softly or indistinctly; "She murmured softly to the
         baby in her arms"
    2: make complaining remarks or noises under one's breath; "she
       grumbles when she feels overworked" [syn: murmur, mutter,
       grumble, croak, gnarl]