Source : Webster's Revised Unabridged Dictionary (1913)

Killer \Kill"er\, n.
   1. One who deprives of life; one who, or that which, kills.

   2. (Zo["o]l.) A voracious, toothed whale of the genus {Orca},
      of which several species are known.

   Note: The killers have a high dorsal fin, and powerful jaws
         armed with large, sharp teeth. They capture, and
         swallow entire, large numbers of seals, porpoises, and
         dolphins, and are celebrated for their savage, combined
         attacks upon the right whales, which they are said to
         mutilate and kill. The common Atlantic species ({Orca
         gladiator}), is found both on the European and the
         American coast. Two species ({Orca ater} and {O.
         rectipinna}) occur on the Pacific coast.

Source : WordNet®

killer
     n 1: someone who causes the death of a person or animal [syn: {slayer}]
     2: the causal agent resulting in death; "heart disease is the
        biggest killer in the United States" [syn: {cause of death}]
     3: a difficulty that is hard to deal with; "that exam was a
        real killer"
     4: predatory black-and-white toothed whale with large dorsal
        fin; common in cold seas [syn: {killer whale}, {orca}, {grampus},
         {sea wolf}, {Orcinus orca}]