Paramour

Part of speech: noun (n.)

1. A lover, of either sex; a wooer or a mistress (formerly in a good sense, now only in a bad one); one who takes the place, without possessing the rights, of a husband or wife; -- used of a man or a woman. The seducer appeared with dauntless front, accompanied by his paramour Macaulay.

2. Love; gallantry. [Obs.] "For paramour and jollity." Chaucer.