radical

American  

[rad-i-kuhl] / ˈræd ɪ kəl /

adjective

1. of or going to the root or origin; fundamental.

   There is a radical difference between the two interpretations of the sacred text, one justifying war and the other requiring nonviolent resistance.

   Synonyms:

   ingrained, innate, original, essential, basic

   Antonyms:

   superficial

2. extreme, especially as regards change from accepted or traditional forms.

   a radical change in the policy of the company.

   Synonyms:

   violent, immoderate, excessive, drastic, thorough, unqualified, complete

   Antonyms:

   superficial

3. favoring drastic political, economic, or social reforms.

   radical ideas;

   radical and anarchistic ideologues.

4. favoring, supporting, or representing extreme forms of religious fundamentalism.

   radical fundamentalists and their rejection of modern science.

5. forming a basis or foundation.

   What is the radical reason for his choice?

6. existing inherently in a thing or person.

   radical defects of character.

7. characterized by a marked departure from prevailing methods, practices, or ideas, particularly in the arts; experimental; unorthodox.

   The composer’s radical approach to sound, using timbre and rhythm rather than pitch, was declared “noise” by an influential critic.

8. Slang. excellent; wonderful; cool; rad.

   You got here on an electric skateboard? That's radical!

9. Mathematics.

   1. pertaining to or forming a root.

   2. denoting or pertaining to the radical sign.

   3. irrational.

10. Grammar. of or pertaining to the root of a word.

11. Botany. of or arising from the root or the base of the stem.

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noun

1. a person who holds or follows strong convictions or extreme principles; extremist.

2. a person who advocates fundamental political, economic, and social reforms by direct and often uncompromising methods.

3. Mathematics.

   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.

4. Chemistry.

   1. group.

   2. free radical.

5. Grammar. root.

6. (in Chinese writing) one of 214 ideographic elements used in combination with phonetics to form thousands of different characters.

radical British  

/ ˈrædɪkəl /

adjective

1. of, relating to, or characteristic of the basic or inherent constitution of a person or thing; fundamental

   a radical fault

2. concerned with or tending to concentrate on fundamental aspects of a matter; searching or thoroughgoing

   radical thought

   a radical re-examination

3. favouring or tending to produce extreme or fundamental changes in political, economic, or social conditions, institutions, habits of mind, etc

   a radical party

4. med (of treatment) aimed at removing the source of a disease

   radical surgery

5. slang very good; excellent

6. of, relating to, or arising from the root or the base of the stem of a plant

   radical leaves

7. maths of, relating to, or containing roots of numbers or quantities

8. linguistics of or relating to the root of a word

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noun

1. a person who favours extreme or fundamental change in existing institutions or in political, social, or economic conditions

2. maths a root of a number or quantity, such as ³√5, √ x

3. Also: radicle.  chem

   1. short for free radical

   2. another name for group

4. linguistics another word for root 1

5. (in logographic writing systems such as that used for Chinese) a part of a character conveying lexical meaning

radical Scientific  

/ răd′ĭ-kəl /

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.

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radical ¹ Cultural  

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

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radical ² Cultural  

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

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Synonym Usage

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, especially in matters of religion or morality, has extravagant views and excessive zeal, rendering that person incapable of sound judgments and prone to take violent action against those who have differing views: fanatical in persecuting others.

Discover More

In general, radicals are associated with chemical reactions that proceed rapidly.

Other Word Forms

• multiradical
  adjective
• nonradical
  adjective
• quasi-radical
  adjective
• radicality
  noun
• radicalness
  noun
• semiradical
  adjective
• subradical
  adjective
• superradical
  adjective
• ultraradical
  adjective
• unradical
  adjective

Etymology

Origin of radical

First recorded in 1350–1400; Middle English, from Late Latin rādīcālis “having roots, forming roots,” from Latin rādīc- (stem of rādix “root”) + -ālis -al ¹; see also root ¹

Explanation

If something is considered extremist or very different from anything that has come before it, call it radical. The noun, radical, comes from the Latin radix "root," and in fact, radical and root are synonymous as technical terms in fields such as math and linguistics. In more everyday language, a radical is someone who has very extreme views, so you could say that their views are different from the root up. Similarly, a radical flaw or change is a fundamental one whereas a radical design or idea is very new and innovative.

Example Sentences

So the first step to make the other person feel loved is to show radical curiosity.

From Los Angeles Times • Jun. 1, 2026

But they had to develop their standards of evidence under conditions of radical uncertainty, without the option of a control group or a repeatable experiment.

From The Wall Street Journal • May 29, 2026

Deirdre Canavan from homelessness charity Depaul called for "radical action" to address what she called a deepening crisis.

From BBC • May 28, 2026

The Baader-Meinhof gang -- named after two early leaders, Andreas Baader and Ulrike Meinhof -- emerged out of the radical fringe of the 1960s and 70s student protest movement.

From Barron's • May 27, 2026

It was the Megalosaurus, and the name was actually suggested to Buckland by his friend Dr. James Parkinson, the would-be radical and eponym for Parkinson’s disease.

From "A Short History of Nearly Everything" by Bill Bryson

Related Words

• agitator
• anarchist
• extremist
• fanatic
• firebrand
• insurgent
• leftist
• militant
• progressive
• rebel
• reformer
• renegade
• revolutionary
• rioter
• subversive