1. A lover, of either gender; a wooer or a mistress: After two days, the parents were informed that their daughter sneaked away with her paramour!
2. A person who takes the place, without possessing the rights, of a husband or wife; referring to a man or a woman: No one knew that Mrs. Robinson had a secret paramour whom she met every weekend!

A paramour can be a lover, especially someone in an adulterous relationship.