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:

Thrasher \Thrash"er\, Thresher \Thresh"er\, n.
   1. One who, or that which, thrashes grain; a thrashing
      machine.
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   2. (Zool.) A large and voracious shark (Alopias vulpes),
      remarkable for the great length of the upper lobe of its
      tail, with which it beats, or thrashes, its prey. It is
      found both upon the American and the European coasts.
      Called also fox shark, sea ape, sea fox, slasher,
      swingle-tail, and thrasher shark.
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   3. (Zool.) A name given to the brown thrush and other allied
      species. See Brown thrush.
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   Sage thrasher. (Zool.) See under Sage.

   Thrasher whale (Zool.), the common killer of the Atlantic.
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WordNet (r) 3.0 (2006):

thrasher
    n 1: a farm machine for separating seeds or grain from the husks
         and straw [syn: thresher, thrasher, threshing
         machine]
    2: thrush-like American songbird able to mimic other birdsongs
       [syn: thrasher, mocking thrush]
    3: large pelagic shark of warm seas with a whiplike tail used to
       round up small fish on which to feed [syn: thresher,
       thrasher, thresher shark, fox shark, Alopius
       vulpinus]