py·re·thrum noun \pī-ˈrē-thrəm, -ˈreth-rəm\
: any of several chrysanthemums with finely divided often aromatic leaves including ornamentals as well as important sources of insecticides
: an insecticide consisting of or derived from the dried heads of any of several Old World chrysanthemums (genus Chrysanthemum of the family Compositae)
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