(n.) One who poisons.

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