'apostatise' originates from Greek, specifically the word 'apostasia', where 'apo-' meant 'away from' and 'stasis' meant 'a standing, departure'.

'apostatise' changed from Late Latin and Medieval Latin 'apostasia' and Old French forms into Middle English 'apostasie' and eventually the modern English verb 'apostatise' (with US variant 'apostatize').

Initially, it meant 'a defection or departure' in the sense of leaving one's position or party; over time it narrowed to the current sense of 'renouncing a faith or cause'.