'prophetically' originates from the adjective 'prophetic' (from Latin 'propheticus'), ultimately from Greek 'prophētēs', where 'pro-' meant 'before' and 'phēmi' meant 'to speak'.

'prophetically' developed from Middle English forms of 'prophetic' (via Old French 'prophetique' and Latin 'propheticus') and was formed by adding the adverbial suffix '-ally' to the adjective 'prophetic' to produce the adverb 'prophetically'.

Initially it related directly to 'pertaining to a prophet' or 'of a prophet'; over time it came to be used more generally as 'having the quality of predicting or foreshadowing' and now means 'in a prophetic manner' (i.e., as if predicting future events).