missouri has 4 distinct synonyms spread across 2 of its 4 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 central United States; a border state during the American Civil War, Missouri was admitted to the Confederacy without actually seceding from the Union
the longest river in the United States; arises in Montana and flows southeastward to become a tributary of the Mississippi at Saint Louis
“The Missouri and Mississippi Rivers together form the third longest river in the world”
Synonyms, antonyms and the broader and narrower relations for missouri come from Princeton University’s WordNet. Full sources and licences.
a member of the Siouan people formerly inhabiting the valley of the Missouri river in Missouri
a dialect of the Chiwere language spoken by the Missouri