The Collaborative International Dictionary of English v.0.48:

Fornicatress \For"ni*ca`tress\, n. [Cf. F. fornicatrice, L.
   fornicatrix.]
   A woman guilty of fornication. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fornicatress
    n 1: a woman adulterer [syn: adulteress, fornicatress,
         hussy, jade, loose woman, slut, strumpet,
         trollop]