'apocalyptically' originates from Greek, specifically the word 'apokalypsis,' where 'apo-' meant 'away' and 'kalyptō' meant 'to cover, to hide'; the adjective/adverb are formed from this root meaning 'revelation' or 'uncovering'.

'apokalypsis' (Greek) passed into Late Latin and Medieval Latin as 'apocalypsis,' then into Middle English as 'apocalypse' (noun). The adjective 'apocalyptic' developed from the noun, and the adverb 'apocalyptically' was formed by adding the adverbial suffix '-ally' to the adjective.

Initially, it meant 'a revelation' or 'an uncovering' (often of divine truth); over time it came to be strongly associated with descriptions of the end of the world and, by extension, anything catastrophic or utterly disastrous—meanings which persist in the modern adverb.