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1. The quality of being adulterous, involving sexual intercourse by a married person with someone other than their spouse.
   "He consequently interprets his own behaviour in sociobiological terms so that, having slept with his ex-wif Charlotte in her current marital bed, he is unnerved not by the adulterousness of the act, which is routine for him, but by the infringement of male territorial boundaries."

Type of: immorality, infidelity, unfaithfulness