pyrethrin

noun

py·​re·​thrin pī-ˈrē-thrən How to pronounce pyrethrin (audio) -ˈre- How to pronounce pyrethrin (audio)
: either of two oily liquid esters C21H28O3 and C22H28O5 having insecticidal properties and occurring especially in the flowers of pyrethrum

Examples of pyrethrin in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Flea and tick prevention for dogs contains chemicals such as pyrethrin, which are toxic to cats. — Jessie Quinn, USA Today, 10 May 2026 He was covered from neck to boots in fabrics soaked with permethrin—a pesticide modelled on the toxic pyrethrin found in chrysanthemum flowers. — Burkhard Bilger, New Yorker, 29 June 2026 Spinosad, although organically certified, can be toxic to bees, and pyrethrins—derived from plants—can affect a wide range of insects. — Anthony Reardon, Kansas City Star, 4 Apr. 2026 The residual sprays can protect your house for up to 45 days, while the pyrethrins, which are short-contact sprays, will irritate the bugs and send them into the residual spray. — Nafeesah Allen, Better Homes & Gardens, 27 Jan. 2026 See All Example Sentences for pyrethrin

Word History

Etymology

International Scientific Vocabulary, from Latin pyrethrum

First Known Use

1882, in the meaning defined above

Time Traveler
The first known use of pyrethrin was in 1882

Browse Nearby Words

pyret-
pyrethrin
pyrethroid
See all Nearby Words

Cite this Entry

“Pyrethrin.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/pyrethrin. Accessed 7 Jul. 2026.

Copy Citation

Medical Definition

pyrethrin

noun
py·​re·​thrin pī-ˈrē-thrən How to pronounce pyrethrin (audio) -ˈreth-rən How to pronounce pyrethrin (audio)
: either of two oily liquid esters C21H28O3 and C22H28O5 that have insecticidal properties and are the active components of pyrethrum

More from Merriam-Webster on pyrethrin

Britannica.com: Encyclopedia article about pyrethrin

Last Updated: - Updated example sentences
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Popular in Grammar & Usage

See More

Is that lie 'bald-faced' or 'bold-faced'?

'A' or 'an'? What about before 'h'? An Indefinite Article Guide

Why is '-ed' sometimes pronounced at the end of a word?

Commonly Misspelled Words

How to Use Em Dashes (—), En Dashes (–) , and Hyphens (-)
See More

Popular in Wordplay

See More

14 Phobias You Probably Haven't Heard Of

The Longest Long Words List

One-Word Oxymorons: Bittersweet, Spendthrift, and More

Ten Words Ending with a Silent ‘T’

12 Lovely and Unusual Words for the Natural World
See More

Popular

See More

Is that lie 'bald-faced' or 'bold-faced'?

14 Phobias You Probably Haven't Heard Of

The Longest Long Words List
See More

Games & Quizzes

See All
Play Quordle: Guess all four words in a limited number of tries. Each of your guesses must be a real 5-letter word.
Quordle Can you solve 4 words at once?
Play Blossom: Solve today's spelling word game by finding as many words as you can using just 7 letters. Longer words score more points.
Blossom Pick the best words!
Play Missing Letter: a crossword with a twist. Each of the 25 puzzle words start with a different letter of the alphabet. Which letter is missing?
The Missing Letter A daily crossword with a twist
hangman letters and game
Hangman Lightning Round Figure out which word fits in the blanks.
See All