concubine

noun3

1. •
   A sexual partner, especially a woman, to whom one is not or cannot be married.
2. •
   A woman who lives with a man, but who is not a wife.

   • And that is more than I will yield unto: / I know I am too mean to be your queen, / And yet too good to be your concubine. — 1591
3. •
   (historical) A slave-girl or woman, kept for instance in a harem, who is held for sexual service.

   • He shall be made a chaste and lustlesse Eunuch, And in my Sarell tend my Concubines: — 1587