(1):

(a.) Pertaining to, or characterized by, apostasy; faithless to moral allegiance; renegade.

(2):

(v. i.) To apostatize.

(3):

(n.) 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.

(4):

(n.) One who, after having received sacred orders, renounces his clerical profession.