WordNet records no synonym and no antonym for aster. 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 chiefly fall-blooming herbs of the genus Aster with showy daisylike flowers
star-shaped structure formed in the cytoplasm of a cell having fibers like rays that surround the centrosome during mitosis
Synonyms, antonyms and the broader and narrower relations for aster come from Princeton University’s WordNet. Full sources and licences.