adultery
n. uncountablen. when a married person has a sexual relationship with someone who is not their husband or wife.
n. a sexual relationship between a married person and someone other than their spouse.
Adultery can end a marriage quickly.
The couple separated after he admitted to adultery with a colleague.
In many legal systems, adultery remains a valid ground for divorce, though its social stigma has diminished significantly in recent decades.
With change of suffix, from the Old French adultere (“violation of conjugal faith”) (in Bernard of Clairvaux, Sermons, 12c.), a learnèd borrowing from Latin adulterium, from adulterō. Replaced the older form avoutrie, from the inherited Old French forms avouterie or aoulterie, while keeping its suffix. Compare French adultère (“adultery”). Displaced Old English ǣwbryċe. Not related to adult.