free radical

noun

: an especially reactive atom or group of atoms that has one or more unpaired electrons
especially : one that is produced in the body by natural biological processes or introduced from an outside source (such as tobacco smoke, toxins, or pollutants) and that can damage cells, proteins, and DNA by altering their chemical structure

Examples of free radical 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.
Electrons can then leak out of the chain, bonding with oxygen in the wrong parts of the mitochondria to form highly reactive free radicals that attack and deform neighboring molecules. — Rowan Jacobsen, Scientific American, 20 Oct. 2026 Its formula features Concentrated Miracle Broth, antioxidant-rich Lime Tea Concentrate, and Clarity Algae to help defend against free radicals and improve discoloration. — Jenny Berg, Vogue, 19 Oct. 2026 Lycopene can help protect blood vessels from the damaging effects of unstable molecules known as free radicals. — Md Published, Verywell Health, 17 Oct. 2026 Damage to mouse cells increased the more they were exposed to these free radicals. — Corinne Purtill, Los Angeles Times, 17 Oct. 2026 See All Example Sentences for free radical

Word History

First Known Use

1870, in the meaning defined above

Time Traveler
The first known use of free radical was in 1870

Rhymes for free radical

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Browse Nearby Words

freer
free radical
free-range
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Cite this Entry

“Free radical.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/free%20radical. Accessed 27 Oct. 2026.

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Medical Definition

free radical

noun
: an especially reactive atom or group of atoms that has one or more unpaired electrons
especially : one that is produced in the body by natural biological processes or introduced from outside (as in tobacco smoke, toxins, or pollutants) and that can damage cells, proteins, and DNA by altering their chemical structure

More from Merriam-Webster on free radical

Britannica.com: Encyclopedia article about free radical

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