pyrethrum

noun

py·re·thrum | \pī-ˈrē-thrəm,

Definition of pyrethrum

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)

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Nymphs can be controlled with insecticidal soap, pyrethrum, rotenone or neem. — Ellen Nibali, baltimoresun.com, "Garden Q&A: Black-eyed Susans with fungal leaf spot disease," 11 July 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'pyrethrum.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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The first known use of pyrethrum was circa 1543

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pyrethrum

noun

py·re·thrum | \pī-ˈrē-thrəm,

-ˈreth-rəm

Medical Definition of pyrethrum

1 : any of several chrysanthemums with finely divided often aromatic leaves including ornamentals as well as important sources of insecticides

2 : an insecticide consisting of or derived from the dried heads of any of several Old World chrysanthemums (genus Chrysanthemum of the family Compositae)