pyrethrum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of several Old World plants of the genus Chrysanthemum, such as C. coccineum, cultivated for their showy flower heads.
2. n. An insecticide made from the dried flower heads of Chrysanthemum cinerariifolium or C. coccineum.

Century Dictionary and Cyclopedia

1. n. A plant of the genus Pyrethrum; feverfew.
2. n. [capitalized] A former genus of composite plants of the tribe Anthemideæ, now included as part of the section Pyrethra in the genus Chrysanthemum, from which it was distinguished by achenes nearly equally from five- to ten-ribbed and crowned with a pappus, characters now known to vary in the same species. The most common species is now called Chrysanthemum Parthenium (for which see feverfew, 1, pellitory, 2, and bertram). Its variety aureum is the golden-feather of the gardens, used for edging.
3. n. A powdered preparation of pyrethrum, used as an insectifuge. Also called pyrethrum-powder. See insect-powder and buhach.
4. n. In pharmacy, the Anacyclus Pyrethrum, or pellitory-of-Spain.

Wiktionary

1. n. Any of several perennial African plants of the genus Chrysanthemum, especially Chrysanthemum cinerariaefolium
2. n. organic chemistry Any of several insecticides obtained from these plants; pyrethrin

WordNet 3.0

1. n. made of dried flower heads of pyrethrum plants
2. n. white-flowered pyrethrum of Balkan area whose pinnate leaves are white and silky-hairy below; source of an insecticide; sometimes placed in genus Chrysanthemum
3. n. used in former classifications for plants later placed in genus Chrysanthemum and now often included in genus Tanacetum
4. n. 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