'antinomic' originates from Greek, specifically the word 'antinomikos', where 'anti-' meant 'against' and 'nomos' meant 'law' or 'custom'.

'antinomikos' changed into Medieval/Latin forms such as 'antinomia'/'antinomicus', passed into Late Latin and French (e.g. French 'antinomique' for the adjective and 'antinomie' for the noun), and then entered English as the noun 'antinomy' and the adjective 'antinomic'.

Initially, it literally meant 'against the law' or 'contrary to law/custom'; over time it came to denote a 'contradiction between equally valid principles' and now commonly means 'involving or producing a contradiction' or more broadly 'self-contradictory'.