WordNet records no synonym and no antonym for coneflower. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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 various plants of the genus Rudbeckia cultivated for their large usually yellow daisies with prominent central cones
a wildflower of the genus Ratibida
Synonyms, antonyms and the broader and narrower relations for coneflower come from Princeton University’s WordNet. Full sources and licences.
any of various perennials of the eastern United States having thick rough leaves and long-stalked showy flowers with drooping rays and a conelike center