disdainful has 11 distinct synonyms spread across 2 of its 2 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
expressing extreme contempt
having or showing arrogant superiority to and disdain of those one views as unworthy
“some economists are disdainful of their colleagues in other social disciplines”
Synonyms, antonyms and the broader and narrower relations for disdainful come from Princeton University’s WordNet. Full sources and licences.