Definition of "pyrethrum"

pyrethrum

/paɪˈɹiθɹəm/

noun
countable and uncountable, plural pyrethrums
1. Any of several daisy-like perennial African plants of the genus Tanacetum, especially Tanacetum cinerariifolium.
  Quotations
  We children would re-tell the stories the following day to other children who worked in the fields picking the pyrethrum flowers, tea-leaves or coffee beans of our European and African landlords.
  1986, Ngũgĩ wa Thiong'o, Decolonising the Mind, Heinemann, published 2005, page 10
2. Anacyclus pyrethrum (pellitory of Spain)
3. (organic chemistry) Any of several insecticides obtained from these plants; pyrethrin.