'apocalyptism' originates from Greek, specifically the word 'apokalypsis', where 'apo-' meant 'away/off' and 'kalyptō' (from which 'kalypsis') meant 'to cover' (so 'apokalypsis' meant 'a revealing' or 'uncovering'); the English noun was formed by adding the suffix '-ism' to the adjective/verb stem.

'apokalypsis' passed into Late Latin as 'apocalypsis', then into Old/Middle French and Middle English as 'apocalypse'/'apocalips', and the modern English formation 'apocalyptism' developed by adding the productive English/Nordic/Latin-derived suffix '-ism' to refer to the doctrine or belief system.

Initially, the root meant 'revelation' or 'uncovering' (a disclosure of hidden things); over time the sense shifted in many contexts to focus specifically on revelations about the end of the world and thus to denote doctrines or attitudes about final catastrophic events, which is the current dominant meaning.