A Meadowe Greene," in a folio of "loose songs" collected by Bishop Percy.
They lay soe close together, they made me much to wonder;
I knew not which was wether, until I saw her under.
Then off he came, and blusht for shame soe soon that he had endit;
Yet still she lies, and to him cryes, "one more and none can mend it."
As a noun meaning "semen or other product of orgasm" it is on record from the 1920s. The sexual cum seems to have no connection with L. cum, the preposition meaning "with, together with," which is occasionally used in English in local names of combined parishes or benifices (e.g. Chorlton-cum-Hardy), in popular Latin phrases (e.g. cum laude), or as a combining word to indicate a dual nature or function (e.g. slumber party-cum-bloodbath).
1731, from Cumæ, from Gk. Kyme, ancient city on the It. coast near Naples, founded by Greeks 8c. B.C.E.; especially famous for the Sybil there, mentioned by Virgil.