Wiktionary
de-christianise
vb. 1 (context transitive English) To make unchristian or non-Christian. 2 (context transitive English) To deprive of the Christian character of. 3 (context transitive English) To remove the Christian aspect of. 4 (context intransitive English) To become un-Christian. 5 (context intransitive English) To renounce one's Christian faith.