star grass has 14 distinct synonyms spread across 3 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.
any of several perennials of the genus Aletris having grasslike leaves and bitter roots reputed to cure colic
any plant of the genus Hypoxis having long grasslike leaves and yellow star-shaped flowers: Africa; Australia; southern Asia; North America
trailing grass native to Europe now cosmopolitan in warm regions; used for lawns and pastures especially in southern United States and India
perennial Australian grass having numerous long spikes arranged like the vanes of a windmill
Synonyms, antonyms and the broader and narrower relations for star grass come from Princeton University’s WordNet. Full sources and licences.