illinois has 4 distinct synonyms spread across 1 of its 3 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.
a midwestern state in north-central United States
a member of the Algonquian people formerly of Illinois and regions to the west
the Algonquian language of the Illinois and Miami
Synonyms, antonyms and the broader and narrower relations for illinois come from Princeton University’s WordNet. Full sources and licences.