skinny has 15 distinct synonyms spread across 3 of its 5 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.
fitting snugly
“a tightly-fitting cover”
giving or spending with reluctance
“our cheeseparing administration”
confidential information about a topic or person
“he wanted the inside skinny on the new partner”
1 of the 5 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for skinny.
Synonyms, antonyms and the broader and narrower relations for skinny come from Princeton University’s WordNet. Full sources and licences.