Source : Webster's Revised Unabridged Dictionary (1913)

Shark \Shark\, n. [Of uncertain origin; perhaps through OF. fr.
   carcharus a kind of dogfish, Gr. karchari`as, so called from
   its sharp teeth, fr. ka`rcharos having sharp or jagged teeth;
   or perhaps named from its rapacity (cf. {Shark}, v. t. & i.);
   cf. Corn. scarceas.]
   1. (Zo["o]l.) Any one of numerous species of elasmobranch
      fishes of the order Plagiostomi, found in all seas.

   Note: Some sharks, as the basking shark and the whale shark,
         grow to an enormous size, the former becoming forty
         feet or more, and the latter sixty feet or more, in
         length. Most of them are harmless to man, but some are
         exceedingly voracious. The man-eating sharks mostly
         belong to the genera {Carcharhinus}, {Carcharodon}, and
         related genera. They have several rows of large sharp
         teeth with serrated edges, as the great white shark
         ({Carcharodon carcharias, or Rondeleti}) of tropical
         seas, and the great blue shark ({Carcharhinus glaucus})
         of all tropical and temperate seas. The former
         sometimes becomes thirty-six feet long, and is the most
         voracious and dangerous species known. The rare
         man-eating shark of the United States coast
         ({Charcarodon Atwoodi}) is thought by some to be a
         variety, or the young, of {C. carcharias}. The dusky
         shark ({Carcharhinus obscurus}), and the smaller blue
         shark ({C. caudatus}), both common species on the coast
         of the United States, are of moderate size and not
         dangerous. They feed on shellfish and bottom fishes.

   2. A rapacious, artful person; a sharper. [Colloq.]

   3. Trickery; fraud; petty rapine; as, to live upon the shark.
      [Obs.] --South.

   {Baskin shark}, {Liver shark}, {Nurse shark}, {Oil shark},
   {Sand shark}, {Tiger shark}, etc. See under {Basking},
      {Liver}, etc. See also {Dogfish}, {Houndfish},
      {Notidanian}, and {Tope}.

   {Gray shark}, the sand shark.

   {Hammer-headed shark}. See {Hammerhead}.

   {Port Jackson shark}. See {Cestraciont}.

   {Shark barrow}, the eggcase of a shark; a sea purse.

   {Shark ray}. Same as {Angel fish}
      (a), under {Angel}.

   {Thrasher} shark, or {Thresher shark}, a large, voracious
      shark. See {Thrasher}.

   {Whale shark}, a huge harmless shark ({Rhinodon typicus}) of
      the Indian Ocean. It becomes sixty feet or more in length,
      but has very small teeth.

Thrasher \Thrash"er\, Thresher \Thresh"er\, n.
   1. One who, or that which, thrashes grain; a thrashing
      machine.

   2. (Zo["o]l.) 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}.

   3. (Zo["o]l.) A name given to the brown thrush and other
      allied species. See {Brown thrush}.

   {Sage thrasher}. (Zo["o]l.) See under {Sage}.

   {Thrasher whale} (Zo["o]l.), the common killer of the
      Atlantic.

Source : WordNet®

thrasher
     n 1: a farm machine for separating seeds or grain from the husks
          and straw [syn: {thresher}, {threshing machine}]
     2: thrush-like American songbird able to mimic other birdsongs
        [syn: {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},
        {thresher shark}, {fox shark}, {Alopius vulpinus}]