pyrethrum

UK: /paɪˈriːθrəm/ US: (pī rē′thrəm, -reth′rəm)

WordReference Random House Unabridged Dictionary of American English © 2026

py•re•thrum  (pī rē′thrəm, -reth′rəm), n. 

1. Plant Biology any of several chrysanthemums, as Chrysanthemum coccineum, having finely divided leaves and showy red, pink, lilac, or white flowers, cultivated as an ornamental.
2. Plant Biology any of several chrysanthemums, as C. cinerariifolium, or C. coccineum, cultivated as a source of insecticides.
3. Drugs [Pharm.] the dried flower heads of these plants, used chiefly as an insecticide and sometimes in medicine for certain skin disorders.

• Greek pýrethron, akin to pyretós fever; compare pellitory
• Latin: pellitory
• 1555–65

Collins Concise English Dictionary © HarperCollins Publishers::

pyrethrum / paɪˈriːθrəm/ noun

1. any of several cultivated Eurasian chrysanthemums, such as Chrysanthemum coccineum and C. roseum, with white, pink, red, or purple flowers
2. any insecticide prepared from the dried flowers of any of these plants, esp C. roseum

Etymology: 16th Century: via Latin from Greek purethron feverfew, probably from puretos fever; see pyretic