a·pos·tate Pronunciation Key (-pstt, -tt)
n.
One who has abandoned one's religious faith, a political party, one's principles, or a cause.The American Heritage® Dictionary of the English Language, Fourth Edition
apostate
\A*pos"tate\, n. [L. apostata, Gr. ?, fr. ?. See Apostasy.] 1. One who has forsaken the faith, principles, or party, to which he before adhered; esp., one who has forsaken his religion for another; a pervert; a renegade.
2. (R. C. Ch.) One who, after having received sacred orders, renounces his clerical profession.
Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.