'antiphrastically' originates from Greek, specifically the word 'antíphrāsis', where 'anti-' meant 'against' and 'phrasis' meant 'speaking'.

'antiphrastically' developed via Latin and Middle English from Greek 'antíphrāsis' -> Latin 'antiphrasis' -> Middle English 'antiphrasis', then the adjective 'antiphrastic' was formed and the adverbial suffix '-ally' (from adjective + -ly) produced 'antiphrastically'.

Initially, it meant 'speaking against (the literal meaning)' in the sense of using opposite words; over time it retained that sense and is now used to mean 'expressing the opposite (often ironically or sarcastically)'.