The Collaborative International Dictionary of English v.0.48:

Exterminator \Ex*ter"mi*na`tor\, n. [L.]
   One who, or that which, exterminates. --Buckle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

exterminator
    n 1: someone who exterminates (especially someone whose
         occupation is the extermination of troublesome rodents and
         insects) [syn: exterminator, terminator, eradicator]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "exterminator":
   Cain, annihilator, apache, arsonist, assassin, assassinator,
   biblioclast, bloodletter, bloodshedder, bomber, bravo, burker,
   burner, butcher, button man, cannibal, cutthroat, demolisher,
   desperado, destroyer, dynamitard, dynamiter, eradicator,
   executioner, garroter, gorilla, gun, gunman, gunsel, hatchet man,
   head-hunter, hit man, homicidal maniac, homicide, hun, iconoclast,
   idol breaker, idoloclast, killer, man-eater, man-killer, manslayer,
   massacrer, matador, murderer, nihilist, pesticide, poison,
   poisoner, ruiner, slaughterer, slayer, strangler, syndicalist,
   terrorist, thug, torpedo, trigger man, vandal, wrecker