free radical

American  

noun

Chemistry, Biochemistry.

1. an atom or molecule that bears an unpaired electron and is extremely reactive, capable of engaging in rapid chain reactions that destabilize other molecules and generate many more free radicals: in the body, deactivated by antioxidants, uric acid, and certain enzyme activities.

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free radical British  

noun

1. Sometimes shortened to: radical.  an atom or group of atoms containing at least one unpaired electron and existing for a brief period of time before reacting to produce a stable molecule Compare group

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free radical Scientific  

1. An atom or group of atoms that has at least one unpaired electron and is therefore unstable and highly reactive. In animal tissues, free radicals can damage cells and are believed to accelerate the progression of cancer, cardiovascular disease, and age-related diseases.

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Etymology

Origin of free radical

First recorded in 1895–1900

Example Sentences

"The free radical process is almost like an explosion or a fire," said Salomon, who is also professor of ophthalmology in the Case Western Reserve School of Medicine.

From Science Daily • Jan. 27, 2026

Seaweed is valued for its antioxidant properties, which helps protect cells against free radical damage.

From Salon • Aug. 5, 2024

“He’s like a free radical, in some sense,” he continued, referring to how Mr. Petzold makes films outside the German film establishment.

From New York Times • Jun. 3, 2023

"These processes improve blood pressure, vascular function, and fight free radical formation. Consequently, clinical studies have shown that berries contribute to lower cardiovascular disease risk."

From Fox News • Feb. 1, 2022

"I always thought a free radical was a political bomb thrower out of jail."

From The Egyptian Cat Mystery by Goodwin, Harold L. (Harold Leland)