floating fern has 6 distinct synonyms spread across 3 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.
aquatic fern of tropical America often used in aquariums
small free-floating aquatic fern from the eastern United States to tropical America; naturalized in western and southern Europe
Synonyms, antonyms and the broader and narrower relations for floating fern come from Princeton University’s WordNet. Full sources and licences.