'antonomastic' originates from Ancient Greek via Late Latin and New Latin, specifically from Greek 'antonomasia' (ἀντωνομασία) where 'anti-' meant 'in place of' and 'onoma' (ὄνομα) meant 'name'.

'antonomastic' developed from the noun 'antonomasia' (borrowed into Late Latin/New Latin) and the English adjective was formed by adding the suffix '-ic' to denote relation to that rhetorical device.

Initially connected directly to the act or device of substituting names ('antonomasia'); over time it has been used adjectivally to describe things relating to, or functioning as, such epithets or substitute names.