Definition of free radical
: 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
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Merriam-Webster unabridged
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Time Traveler for free radical
The first known use of free radical was in 1870
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