one who abandons his religious faith or political beliefs
I was a passionate communist from the age of fourteen, but became an apostate at twenty-five.
apo (away from) stenai (to stand) (Greek)
apostate can be thought of as 'opposite state'. That is changing to the opposite state, and not loyal to his current state. apostate ~ apo + state; Prefix 'apo' means away; so away from state: One who's away from his state or religion. (Abandonment of religious values) Apostles do not apostate