Any plant of the genus Helianthus; -- so called probably from the form and color of its flower, which is large disk with yellow rays. The commonly cultivated sunflower is Helianthus annuus, a native of America. [1913 Webster]
sunflower, n. any very tall plant of the genus Helianthus, esp. H. annus with very large showy golden-rayed flowers, grown also for its seeds which yield an edible oil.