Verb
To renounce totally a religious belief once professed; to forsake one's church, the faith or principles once held, or the party to which one has previously adhered.
Source: Webster's dictionary[M]y friends and I are totally at a loss to understand the new form of the Mass... Every attendance at Mass leaves me without comfort or edification. I shall never, pray God, apostatize but church-going is now a bitter trial. Evelyn Waugh