SUN'FLOWER, noun [sun and flower.] A plant of the genus Helianthus; so called from the form and color of its flower, or from its habit of turning to the sun. The bastard sunflower is of the genus Helenium; the dwarf sunflower is of the genus Rudbeckia, and another of the genus Tetragonotheca; the little sunflower is of the genus Cistus.