Paramour

[par-uh-moo r] /ˈpær əˌmʊər/

noun
1.
an illicit lover, especially of a married person.
2.
any lover.
/ˈpærəˌmʊə/
noun
1.
(mainly derogatory) a lover, esp an adulterous woman
2.
an archaic word for beloved (sense 2)
n.

c.1300, noun use of adverbial phrase par amour (c.1300) “passionately, with strong love or desire,” from Anglo-French and Old French par amour, from accusative of amor “love,” from amare “to love” (see Amy). Originally a term for Christ (by women) or the Virgin Mary (by men), it came to mean “darling, sweetheart” (mid-14c.) and “mistress, concubine, clandestine lover” (late 14c.).