The Collaborative International Dictionary of English v.0.48:

Adulterer \A*dul"ter*er\, n. [Formed fr. the verb adulter, with
   the E. ending -er. See Advoutrer.]
   1. A man who commits adultery; a married man who has sexual
      intercourse with a woman not his wife.
      [1913 Webster]

   2. (Script.) A man who violates his religious covenant.
      --Jer. ix. 2.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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