- adulterous, extramarital, extracurricular - characterized by adultery; "an adulterous relationship"; "extramarital affairs"; "the extracurricular activities of a philandering husband"
Antonym: licit (indirect, via illicit)
- adulterous, cheating, two-timing - not faithful to a spouse or lover; "adulterous husbands and wives"; "a two-timing boyfriend"
Antonym: faithful (indirect, via unfaithful)