'antonymic' originates from Greek, specifically the word 'antonymon', where 'anti-' meant 'against, opposite' and 'onoma' (name) meant 'name'. The adjective is formed by adding the suffix '-ic' (from Greek/Latin) to the noun.

'antonymic' developed from the Greek 'antonymon' (literally 'opposite name') which passed into Modern Latin/English as 'antonym' and then took the adjective-forming suffix '-ic' to become 'antonymic' in modern English.

Initially it was built on the idea of an 'opposite name' for words; over time it came to mean 'relating to antonyms' or 'characteristic of oppositeness in meaning'.