misteress

Etymology
.

Noun

 * 1)  A male partner in an extramarital relationship; a male paramour; a kept man.
 * 2) * 2001, Wise, Wonder..., iUniverse (2001), Writers Club Press (2001), ISBN 059518829X, page 135:
 * He had a long-standing relationship with his married female CEO boss, and in his eyes, had sex for salary. In her eyes, he was a convenient misteress.