Paramour (noun)

A lover, especially one who is not a spouse.

Origin:

Derived from the old french word "par amour" meaning "by love", the word "paramour" came into use in the 14th century.

Examples:

1. He had a paramour on the side.
2. The paramour was not aware of his marriage.
3. The paramour was kept a secret from the wife.
4. Paramour is a word that is often used to describe a romantic partner in a secret or illicit relationship.
5. The term is often used to describe a person that one is having an extramarital affair with.