The Collaborative International Dictionary of English v.0.48:

Song \Song\ (s[o^]ng; 115), n. [AS. song, sang, fr. singan to
   sing; akin to D. zang, G. sang, Icel. s["o]ngr, Goth. saggws.
   See Sing.]
   1. That which is sung or uttered with musical modulations of
      the voice, whether of a human being or of a bird, insect,
      etc. "That most ethereal of all sounds, the song of
      crickets." --Hawthorne.
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   2. A lyrical poem adapted to vocal music; a ballad.
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   3. More generally, any poetical strain; a poem.
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            The bard that first adorned our native tongue
            Tuned to his British lyre this ancient song.
                                                  --Dryden.
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   4. Poetical composition; poetry; verse.
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            This subject for heroic song.         --Milton.
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   5. An object of derision; a laughingstock.
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            And now am I their song, yea, I am their byword.
                                                  --Job xxx. 9.
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   6. A trifle; an insignificant sum of money; as, he bought it
      for a song. "The soldier's pay is a song." --Silliman.
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   Old song, a trifle; nothing of value. "I do not intend to
      be thus put off with an old song." --Dr. H. More.

   Song bird (Zool.), any singing bird; one of the Oscines.


   Song sparrow (Zool.), a very common North American sparrow
      (Melospiza fasciata, or Melospiza melodia) noted for
      the sweetness of its song in early spring. Its breast is
      covered with dusky brown streaks which form a blotch in
      the center.

   Song thrush (Zool.), a common European thrush (Turdus
      musicus), noted for its melodius song; -- called also
      mavis, throstle, and thrasher.
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   Syn: Sonnet; ballad; canticle; carol; canzonet; ditty; hymn;
        descant; lay; strain; poesy; verse.
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The Collaborative International Dictionary of English v.0.48:

Mavis \Ma"vis\ (m[=a]"v[i^]s), n. [F. mauvis, Arm. milvid,
   milfid, milc'hhouid, Corn. melhuez.] (Zool.)
   The European throstle or song thrush (Turdus musicus).
   [1913 Webster] Mavournin

WordNet (r) 3.0 (2006):

mavis
    n 1: common Old World thrush noted for its song [syn: song
         thrush, mavis, throstle, Turdus philomelos]