Definition of "Pyrethrum" :

noun: used in former classifications for plants later placed in genus Chrysanthemum and now often included in genus Tanacetum

noun: spring-flowering garden perennial of Asiatic origin having finely divided aromatic leaves and white to pink-purple flowers; source of an insecticide; sometimes placed in genus Chrysanthemum

noun: white-flowered pyrethrum of Balkan area whose pinnate leaves are white and silky-hairy below; source of an insecticide; sometimes placed in genus Chrysanthemum

noun: made of dried flower heads of pyrethrum plants