buckthorn has 6 distinct synonyms 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.
a shrub or shrubby tree of the genus Rhamnus; fruits are source of yellow dyes or pigments
Synonyms, antonyms and the broader and narrower relations for buckthorn come from Princeton University’s WordNet. Full sources and licences.
any shrub or small tree of the genus Bumelia
an Old World plantain with long narrow ribbed leaves widely established in temperate regions