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[rad-i-kuh l] /ˈræd ɪ kəl/
of or going to the root or origin; fundamental:
a radical difference.
thoroughgoing or extreme, especially as regards change from accepted or traditional forms:
a radical change in the policy of a company.
favoring drastic political, economic, or social reforms:
radical ideas; radical and anarchistic ideologues.
favoring, supporting, or representing extreme forms of religious fundamentalism:
radical fundamentalists and their rejection of modern science.
forming a basis or foundation:
What is the radical reason for his choice?
existing inherently in a thing or person:
radical defects of character.
  1. pertaining to or forming a root.
  2. denoting or pertaining to the radical sign.
  3. irrational (def 5b).
Grammar. of or pertaining to the root of a word.
Botany. of or arising from the root or the base of the stem.
a person who holds or follows strong convictions or extreme principles; extremist.
a person who advocates fundamental political, economic, and social reforms by direct and often uncompromising methods.
  1. a quantity expressed as a root of another quantity.
  2. the set of elements of a ring, some power of which is contained in a given ideal.
  3. radical sign.
  1. group (def 3).
  2. free radical.
Grammar. root1 (def 12).
(in Chinese writing) one of 214 ideographic elements used in combination with phonetics to form thousands of different characters.
Origin of radical
1350-1400; Middle English < Late Latin rādīcālis “having roots,” equivalent to Latin rādīc- (stem of rādīx) root1 + -ālis -al1
Related forms
radicalness, noun
multiradical, adjective
nonradical, adjective, noun
quasi-radical, adjective
semiradical, adjective
subradical, adjective
superradical, adjective
ultraradical, adjective, noun
unradical, adjective
1. basic, essential; original, innate, ingrained. 2. complete, unqualified, thorough; drastic, excessive, immoderate, violent.
1, 2. superficial.
Synonym Study
2.Radical, extreme, fanatical denote that which goes beyond moderation or even to excess in opinion, belief, action, etc. Radical emphasizes the idea of going to the root of a matter, and this often seems immoderate in its thoroughness or completeness: radical ideas; radical changes or reforms. Extreme applies to excessively biased ideas, intemperate conduct, or repressive legislation: to use extreme measures. Fanatical is applied to a person who has extravagant views, especially in matters of religion or morality, which render that person incapable of sound judgments; and excessive zeal which leads him or her to take violent action against those who have differing views: fanatical in persecuting others. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for radical
Contemporary Examples
Historical Examples
  • The difference too is radical; it goes to the heart of the mystery.

    'Tis Sixty Years Since Charles Francis Adams
  • The influence of Westhampton is radical, and fills the Council with a lot of outsiders.

    Viviette William J. Locke
  • "Yes, by that radical miller who lives at Martover," said Marion.

    The Coryston Family Mrs. Humphry Ward
  • For in his growth as a radical, Joe had gone beyond all arguing now.

    The Harbor Ernest Poole
  • For under all her radical talk Sue had the kindest heart in the world.

    The Harbor Ernest Poole
British Dictionary definitions for radical


of, relating to, or characteristic of the basic or inherent constitution of a person or thing; fundamental: a radical fault
concerned with or tending to concentrate on fundamental aspects of a matter; searching or thoroughgoing: radical thought, a radical re-examination
favouring or tending to produce extreme or fundamental changes in political, economic, or social conditions, institutions, habits of mind, etc: a radical party
(med) (of treatment) aimed at removing the source of a disease: radical surgery
(slang, mainly US) very good; excellent
of, relating to, or arising from the root or the base of the stem of a plant: radical leaves
(maths) of, relating to, or containing roots of numbers or quantities
(linguistics) of or relating to the root of a word
a person who favours extreme or fundamental change in existing institutions or in political, social, or economic conditions
(maths) a root of a number or quantity, such as ³√5, √x
(chem) Also radicle
  1. short for free radical
  2. another name for group (sense 10)
(linguistics) another word for root1 (sense 9)
(in logographic writing systems such as that used for Chinese) a part of a character conveying lexical meaning
Derived Forms
radicalness, noun
Word Origin
C14: from Late Latin rādīcālis having roots, from Latin rādix a root
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
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Word Origin and History for radical

late 14c., in a medieval philosophical sense, from Late Latin radicalis "of or having roots," from Latin radix (genitive radicis) "root" (see radish). Meaning "going to the origin, essential" is from 1650s. Radical sign in mathematics is from 1680s.

Political sense of "reformist" (via notion of "change from the roots") is first recorded 1802 (n.), 1817 (adj.), of the extreme section of the British Liberal party (radical reform had been a current phrase since 1786); meaning "unconventional" is from 1921. U.S. youth slang use is from 1983, from 1970s surfer slang meaning "at the limits of control." Radical chic is attested from 1970; popularized, if not coined, by Tom Wolfe. Radical empiricism coined 1897 by William James (see empiricism).


1630s, "root part of a word, from radical (adj.) Political sense from 1802; chemical sense from 1816.

Online Etymology Dictionary, © 2010 Douglas Harper
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radical in Medicine

radical rad·i·cal (rād'ĭ-kəl)
Abbr. R

  1. A group of elements or atoms usually passing intact from one compound to another but generally incapable of prolonged existence in a free state.

  2. A free radical.

  1. Of or being medical treatment by extreme, drastic, or innovative measures.

  2. Designed to act on or eliminate the root or cause of a pathological process.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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radical in Science
  1. A root, such as √2, especially as indicated by a radical sign (√).

  2. A group of atoms that behaves as a unit in chemical reactions and is often not stable except as part of a molecule. The hydroxyl, ethyl, and phenyl radicals are examples. Radicals are unchanged by chemical reactions.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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radical in Culture

radical definition

In politics, someone who demands substantial or extreme changes in the existing system.

radical definition

In chemistry, an atom or group of atoms that has at least one electron free to participate in forming a chemical bond.

Note: In general, radicals are associated with chemical reactions that proceed rapidly.
The New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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