The Collaborative International Dictionary of English v.0.48:

Fornicator \For"ni*ca`tor\, n. [F. fornicateur, OF. fornicator,
   from L. fornicator.]
   An unmarried person, male or female, who has criminal
   intercourse with the other sex; one guilty of fornication.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fornicator
    n 1: someone who commits adultery or fornication [syn:
         adulterer, fornicator]