1650s, "distinctive of either sex, of or pertaining to the fact of being male or female," from Late Latin sexualis "relating to sex," from Latin sexus "a sex, state of being either male or female, gender" (see sex (n.)).
The meaning "pertaining to copulation or generation" is from 1766, on the notion of "done by means of the two sexes;" hence also "pertaining to erotic appetites and their gratification" and "peculiar to or affecting the organs of sex, venereal" (1799). The phrase sexual intercourse is attested by 1771 (see intercourse), sexual orientation by 1967, sexual harassment by 1975. Sexual revolution is attested by 1962. Sexual politics is from 1970. Related: Sexually.
<a href="https://www.etymonline.com/word/unisexual">Etymology of unisexual by etymonline</a>
Harper, D. (n.d.). Etymology of unisexual. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/unisexual