Adjective

1. adulterous, extramarital, extracurricular, illicit (vs. licit)

usage: characterized by adultery; "an adulterous relationship"; "extramarital affairs"; "the extracurricular activities of a philandering husband"

2. adulterous, cheating(prenominal), two-timing(prenominal), unfaithful (vs. faithful)

usage: not faithful to a spouse or lover; "adulterous husbands and wives"; "a two-timing boyfriend"

See also: adulterous (Dictionary)