prickly poppy has 4 distinct synonyms spread across 2 of its 2 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 plant of the genus Argemone having large white or yellow flowers and prickly leaves and stems and pods; chiefly of tropical America
annual Old World poppy with orange-red flowers and bristly fruit
Synonyms, antonyms and the broader and narrower relations for prickly poppy come from Princeton University’s WordNet. Full sources and licences.