Adultery (noun)

1. Voluntary sexual intercourse between a married person and someone other than their spouse.
2. An act of unfaithfulness to a spouse.

Origin:

From the latin word "adulterium" meaning "illicit sexual intercourse".

Examples:

1. Adultery is considered a serious offence in many cultures and religions.
2. The revelation of his wife's adultery came as a shock to him.
3. Many people believe that adultery is morally wrong and can lead to the breakdown of a marriage.
4. He was accused of committing adultery with his secretary.
5. Adultery is grounds for divorce in many jurisdictions.