'oppositeness' originates from Latin, specifically the word 'oppositus' (past participle of 'opponere'), where 'ob-' (later 'op-') meant 'toward' and 'ponere' meant 'to place'.

'oppositus' passed into Late Latin and Old French forms related to 'opposé' and Middle English adopted these into the adjective 'opposite', to which the noun-forming suffix '-ness' was later added to create 'oppositeness'.

Initially, the root meant 'placed against' or 'set opposite'; over time it came to denote the abstract idea of being 'contrary' or 'in opposition', and the modern noun 'oppositeness' denotes that state or quality.