adultery Play /əˈdəlt(ə)ri/nounVoluntary sexual intercourse between a married person and a person who is not his or her spouse.she was committing adultery with a much younger manunfaithfulness,infidelity,falseness,disloyalty,unchastity,cuckoldry,extramarital sex,extramarital relations SYNONYMS cuckoldrydisloyaltyextramarital relationsextramarital sexfalsenessinfidelityunchastityunfaithfulness