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free radical

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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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Compare diradical.

Origin of free radical

First recorded in 1895–1900
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for free radical

free radical

noun
  1. 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 moleculeSometimes shortened to: radical Compare group (def. 10)
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

free radical in Medicine

free radical

n.
  1. An uncharged atom or group of atoms having at least one unpaired electron, which makes it highly reactive.
  2. An organic compound having some unpaired valence electrons; a normal byproduct of oxidation reactions in metabolism.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

free radical in Science

free radical

  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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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.