'antonymy' is formed from the noun 'antonym' + the suffix '-y' (forming a state or condition). 'Antonym' ultimately comes from Greek 'antōnymon', where 'anti-' meant 'against, opposite' and 'onoma' (or 'onym-') meant 'name'.

'antonym' was coined from Greek 'antōnymon' and entered English in the 19th century; later the formation 'antonym' + '-y' produced 'antonymy' to denote the condition or relationship, yielding the modern English word 'antonymy'.

Initially the elements referred to 'opposite name' or 'opposite word', and over time the compound came to denote the linguistic relation of words having opposite meanings (the current sense of 'antonymy').