APOSTATE

adj. guilty of apostasy (abandonment of religious vows or values)

n. one who is guilty of committing heresy; traitor

Apostasy (from Greek αποστασία, meaning a defection or revolt, from απο, apo, "away, apart", στασις, stasis, "standing") is a term generally employed to describe the formal abandonment or renunciation of one's religion, especially if the motive is deemed unworthy. In a technical sense, as used sometimes by sociologists without the pejorative connotations of the word, the term refers to renunciation and criticism of, or opposition to one's former religion. One who commits apostasy is an apostate, or one who apostatises. Apostasy is generally not a self-definition: very few former believers call themselves apostates and they generally consider this term to be a pejorative. One of the possible reasons for this renunciation is loss of faith, another is the failure of alleged religious indoctrination or brainwashing.
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Noun
1. a disloyal person who betrays or deserts his cause or religion or political party or friend etc.
(synonym) deserter, renegade, turncoat, recreant, ratter
(hypernym) quitter
(derivation) apostatize, apostatise, tergiversate
Adjective
1. not faithful to religion or party or cause
(similar) unfaithful

n. apostate, backslider, renegade, one who abandons a religion

v. compete, contend against another, participate in a contest

v. apostatize, fall away