Pronunciation: (pī-rē'thrum, -reth'rum),[key] —n. 1. any of several chrysanthemums, as Chrysanthemum coccineum, having finely divided leaves and showy red, pink, lilac, or white flowers, cultivated as an ornamental.
2. any of several chrysanthemums, as C. cinerariifolium, or C. coccineum, cultivated as a source of insecticides.
3. Pharm.the dried flower heads of these plants, used chiefly as an insecticide and sometimes in medicine for certain skin disorders.