grass has 28 distinct synonyms spread across 6 of its 11 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.
narrow-leaved green herbage: grown as lawns; used as pasture for grazing animals; cut and dried as hay
German writer of novels and poetry and plays (born 1927)
Synonyms, antonyms and the broader and narrower relations for grass come from Princeton University’s WordNet. Full sources and licences.