'vermifugal' originates from Latin, specifically the word 'vermifugus', where 'vermi-' (from 'vermis') meant 'worm' and 'fugus' (from 'fugare'/'fugere') meant 'to drive away or flee'.

'vermifugus' in Latin gave rise to forms like Old French 'vermifuge' and English 'vermifuge' (a noun meaning a substance that expels worms); the adjective 'vermifugal' and its adverbial form 'vermifugally' were formed in English from these roots.

Initially it meant 'driving away worms' in a literal sense; over time it became a technical/medical term referring to substances or actions that expel or destroy intestinal parasites, and now also functions as an adjective/adverb in that sense.