Merriam-Webster Collegiate Dictionary - pyrethrum

 noun  Etymology: Latin, pellitory, from Greek pyrethron, from pyr fire  Date: circa 1543  1. any of several chrysanthemums with finely divided often aromatic leaves including ornamentals as well as important sources of insecticides  2. an insecticide made from the dried heads of any of several Old World chrysanthemums (especially Chrysanthemum cinerariaefolium)