poisoner

from WordNet (r) 3.0 (2006)

poisoner
    n 1: someone who kills with poison

from The Collaborative International Dictionary of English v.0.48

Poisoner \Poi"son*er\, n.
   One who poisons. --Shak.
   [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

41 Moby Thesaurus words for "poisoner":
      Cain, apache, assassin, assassinator, bloodletter, bloodshedder,
      bravo, burker, butcher, button man, cannibal, cutthroat, desperado,
      eradicator, executioner, exterminator, garroter, gorilla, gun,
      gunman, gunsel, hatchet man, head-hunter, hit man,
      homicidal maniac, homicide, killer, man-eater, man-killer,
      manslayer, massacrer, matador, murderer, pesticide, poison,
      slaughterer, slayer, strangler, thug, torpedo, trigger man