adultery

Sexual intercourse by a married person with someone other than their spouse. See more synonyms at Thesaurus:cuckoldry

She engaged in adultery because her spouse has a low libido, while hers is very high.

So also that copulation which in one City is Matrimony, in another will be judged Adultery.

Lewdness or unchastity of thought as well as act, as forbidden by the sixth/seventh commandment; sinful sexual behavior as a category.

Thou shalt not commit adultery.

Faithlessness in religion.

And it came to pass through the lightness of her whoredom, that she defiled the land, and committed adultery with stones and with stocks.

The fine and penalty formerly imposed for the offence of adultery.

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