pyrethrin

noun py·re·thrin \ pī-ˈrē-thrən , -ˈre- \

|Updated on: 20 May 2018

Definition of pyrethrin

: either of two oily liquid esters C₂₁H₂₈O₃ and C₂₂H₂₈O₅ having insecticidal properties and occurring especially in the flowers of pyrethrum

Recent Examples of pyrethrin from the Web

As if that's not reason enough to avoid them, those insecticidal shampoos often don't even work any more, because so many lice have also become resistant to pyrethrins and pyrethroids.

— mariko zapf, Good Housekeeping, "This 3-Step Natural Head Lice Remedy Works For My Family Every Time," 15 Aug. 2017
Most wasp killers contain pyrethrins, which are derived from botanical sources.

— joan morris, The Mercury News, "Wasps using agapanthus as a home base," 28 Mar. 2017
The Extension recommends using a fast-acting aerosol insecticide containing pyrethrins if fire ants are detected among flood debris, though these insecticides can be toxic to aquatic organisms, so caution is recommended.

— jonece starr dunigan, AL.com, "Burning smell prompts plane to land at Selma airport, 2 injured," 21 June 2017
Pyrethrins and pyrethroids also work by interfering with sodium pores.

— karen weintraub, Scientific American, "Revenge of the Super Lice," 29 May 2017

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