meniscus has 1 distinct synonym 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.
(anatomy) a disk of cartilage that serves as a cushion between the ends of bones that meet at a joint
(optics) a lens that is concave on one side and convex on the other
(physics) the curved upper surface of a nonturbulent liquid in a vertical tube
Synonyms, antonyms and the broader and narrower relations for meniscus come from Princeton University’s WordNet. Full sources and licences.