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.
Formulated with antioxidant vitamin E to help defend against surface free radicals, this product locks in moisture to hydrate the skin without leaving a greasy residue and dries completely matte upon application. — Alison Abbey Hudak, Footwear News, 1 Sep. 2026 Antioxidants are compounds found in fruits and vegetables that contribute to their bright colors and help protect the body from damage caused by free radicals. — Ashley Olivine, Verywell Health, 27 Aug. 2026 Kash says they are packed with antioxidants such as polyphenols and flavonoids to neutralize free radicals that cause stress and inflammation and help with boosting your immune system overall. — Marie Bladt, Vogue, 11 Aug. 2026 We can be exposed to free radicals from a number of sources including cigarette smoke, air pollution, sunlight, and even exercise. — Isabel Vasquez Rd Ldn, HEALTH, 11 Aug. 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 5 Sep. 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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