'antithesis' originates from Greek, specifically the word 'antithesis' (ἀντίθεσις), where 'anti-' meant 'against' and 'tithenai' (or the root related to 'thesis') meant 'to place'.

'antithesis' passed into Latin as 'antithesis', then into Late Latin/Medieval Latin and Middle English, eventually becoming the modern English word 'antithesis' (plural 'antitheses').

Initially, it meant 'a placing against' (a setting in opposition); over time it evolved to mean 'a direct contrast or opposite', which is its current common meaning.