paramour

(old-fashioned) A person (especially someone who is not one's spouse) with whom one has an illicit or secret affair; also (Scotland, US, law), one with whom a married person has an adulterous affair.

(historical) A woman who is the object of a knight's love, and who he fights for.

(no longer used) A person who is the object of one's love, especially in an affair or romance; a lover; also, a sexual partner.

(no longer used) God as the object of a person's devotion or love.

(no longer used) Of loving, etc.: out of or through romantic feeling or sexual desire; passionately.

(no longer used) Used chiefly when addressing someone: out of or through devotion or kindness; as a favour or kindness.

(old-fashioned) To have an illicit or secret affair with a person, especially someone who is not one's spouse.