WordNet records no synonym and no antonym for magnolia. 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.
dried bark of various magnolias; used in folk medicine
any shrub or tree of the genus Magnolia; valued for their longevity and exquisite fragrant blooms
Synonyms, antonyms and the broader and narrower relations for magnolia come from Princeton University’s WordNet. Full sources and licences.