early 19c. U.S. colloquial, "a female, a woman," from she + male.
Davy Crockett's hand would be sure to shake if his iron was pointed within a hundred miles of a shemale. ["Treasury of American Folklore"]This became obsolete, and by 1972 it had been recoined (disparagingly) for "masculine lesbian." The sense of "transsexual male" seems to date from c. 1984.