WordNet records no synonym and no antonym for henry iii. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
son of Henry II of France and the last Valois to be king of France (1551-1589)
son of King John and king of England from 1216 to 1272; his incompetence aroused baronial opposition led by Simon de Montfort (1207-1272)
Synonyms, antonyms and the broader and narrower relations for henry iii come from Princeton University’s WordNet. Full sources and licences.