Yours, Etc.: Origins and Uses of 8 Sign-Offs
early 15c., disaperen, from dis- "do the opposite of" + appear. Earlier was disparish (early 15c.), from French disparaiss-, stem of disparaître. Related: Disappeared; disappearing; disappears. Slang disappearing act is originally of magic shows; in figurative sense of "getting away" first attested 1913.