pluto has 3 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 cartoon character created by Walt Disney
(Roman mythology) god of the underworld; counterpart of Greek Hades
a large asteroid that was once thought to be the farthest known planet from the sun; it has an elliptical orbit
“Pluto was discovered by Clyde Tombaugh in 1930”
Synonyms, antonyms and the broader and narrower relations for pluto come from Princeton University’s WordNet. Full sources and licences.