late 14c. (harmofroditus), from Latin hermaphroditus, from Greek hermaphroditos "person partaking of the attributes of both sexes," as a proper name, the son of Hermes and Aphrodite, who, in Ovid, was loved by the nymph Salmacis so ardently that she prayed for complete union with him and as a result they were united bodily, combining male and female characteristics.
Also used figuratively in Middle English of "one who improperly occupies two offices." As a name for the condition, Middle English had hermofrodito (late 14c.), hermofrodisia (early 15c.). As an adjective, from c. 1600. Also used of things of two natures, such as hermaphrodite brig, for a vessel square-masted fore and schooner-rigged aft.
"a lesbian," especially one considered tough, mannish, or aggressive, 1931, American English, perhaps a shortening of morphadike, a dialectal garbling of hermaphrodite; but bulldyker "engage in lesbian activities" is attested from 1921. According to "Dictionary of American Slang," a source from 1896 lists dyke as slang for "the vulva," and Farmer and Henley ("Slang and Its Analogues," 1893) has "hedge on the dyke" for "the female pubic hair."
[T]he word appears first in the long forms, bulldiker and bulldyking, both used in the 1920s by American blacks. No African antecedents have been found for the term, however, which leads to the possibility that this is basically just another backcountry, barnyard word, perhaps a combination of BULL and DICK. [Rawson]