adultery

n. infidelity, fornication, sexual relations with someone other than one's spouse

Adultery is voluntary sexual intercourse between a married person and one who is not his or her spouse. Some legal jurisdictions have defined it as "crime against marriage", opposed to infidelity.
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Noun
1. extramarital sex that willfully and maliciously interferes with marriage relations; "adultery is often cited as grounds for divorce"
(synonym) criminal conversation, fornication
(hypernym) extramarital sex, free love

(n.)
The unfaithfulness of a married person to the marriage bed; sexual intercourse by a married man with another than his wife, or voluntary sexual intercourse by a married woman with another than her husband.
  

(n.)
The intrusion of a person into a bishopric during the life of the bishop.
  

(n.)
The fine and penalty imposed for the offense of adultery.
  

(n.)
Lewdness or unchastity of thought as well as act, as forbidden by the seventh commandment.
  

(n.)
Injury; degradation; ruin.
  

(n.)
Faithlessness in religion.
  

(n.)
Adulteration; corruption.
  

Voluntary sexual intercourse between a married person and another person who is not their married spouse. - (read more on Adultery)