WordNet (r) 3.0 (2006):

rapist
    n 1: someone who forces another to have sexual intercourse [syn:
         raper, rapist]

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "rapist":
   Mafioso, Young Turk, beast, beldam, berserk, berserker, betrayer,
   bomber, brute, bugger, coprophiliac, debaucher, deceiver, defiler,
   demon, despoiler, devil, dragon, erotomaniac, exhibitionist,
   fetishist, fiend, fire-eater, firebrand, fury, goon, gorilla,
   gunsel, hardnose, hell-raiser, hellcat, hellhound, hellion,
   holy terror, hood, hoodlum, hothead, hotspur, incendiary, killer,
   mad dog, madcap, masochist, monster, mugger, narcissist,
   necrophiliac, nymphomaniac, paraphiliac, pederast, pedophiliac,
   raper, ravager, ravisher, revolutionary, sadist, satyr, savage,
   scotophiliac, seducer, she-wolf, sodomist, sodomite, spitfire,
   termagant, terror, terrorist, tiger, tigress, tough, tough guy,
   transvestite, ugly customer, violator, violent, virago, vixen,
   voyeur, wild beast, witch, wolf, zoophiliac