"adulterous" in the adjective sense
1. adulterous, extramarital, extracurricular
characterized by adultery
"an adulterous relationship"
"extramarital affairs"
"the extracurricular activities of a philandering husband"
2. adulterous, cheating, two-timing
not faithful to a spouse or lover
"adulterous husbands and wives"
"a two-timing boyfriend"
Source: WordNet® (An amazing lexical database of English)
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