Source : Webster's Revised Unabridged Dictionary (1913)

Murderer \Mur"der*er\, n.
   1. One guilty of murder; a person who, in possession of his
      reason, unlawfully kills a human being with premeditated
      malice.

   2. A small cannon, formerly used for clearing a ship's decks
      of boarders; -- called also {murdering piece}. [Obs.]

Source : WordNet®

murderer
     n : a criminal who commits homicide (who performs the unlawful
         premeditated killing of another human being) [syn: {liquidator},
          {manslayer}]