[syn: adulterous, cheating(a), two-timing(a)]
The Collaborative International Dictionary of English v.0.48:
Adulterous \A*dul"ter*ous\, a.
   1. Guilty of, or given to, adultery; pertaining to adultery;
      illicit. --Dryden.
      [1913 Webster]
   2. Characterized by adulteration; spurious. "An adulterous
      mixture." [Obs.] --Smollett.
      [1913 Webster]
WordNet (r) 3.0 (2006):
adulterous
    adj 1: characterized by adultery; "an adulterous relationship";
           "extramarital affairs"; "the extracurricular activities
           of a philandering husband" [syn: adulterous,
           extramarital, extracurricular]
    2: not faithful to a spouse or lover; "adulterous husbands and
       wives"; "a two-timing boyfriend" [syn: adulterous,
       cheating(a), two-timing(a)]