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.

---

noun

• radicals
  plural

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

---

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.

---

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.

---

radical ² Cultural  

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

---

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

Derived Forms

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

Inflected Forms

Nouns

• radicals
  plural

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

See Examples For:

radical radicals

Mitchell’s self-imposed moderation might not look radical at first.

From Salon ● Aug. 20, 2026

Prof Heide-Jørgensen, from the Greenland Institute of Natural Resources, told BBC News that the changes in the region were "probably the most radical we can see anywhere in the subarctic".

From BBC ● Aug. 20, 2026

Tommy John, who ruptured a ligament in his left elbow in 1974, agreed to a radical surgery that revived his career and changed baseball.

From Los Angeles Times ● Aug. 16, 2026

But it was his radical reforms as premier from 1998 that cemented his reputation as a no-compromise free marketeer.

From Barron's ● Aug. 12, 2026

And if the early Martin Luther King, Jr., was a bit too radical for their tastes, they viewed the Royal Ice Cream Parlor sit-ins led by Douglas Moore with something akin to horror.

From "The Best of Enemies" by Osha Gray Davidson

By pinpointing hydrogen radicals as a dominant force, scientists now have a clearer picture of the chemistry involved.

From Science Daily ● Jun. 16, 2026

In the 1960s and ’70s, communal radicals and intellectuals such as E.F.

From The Wall Street Journal ● Jun. 2, 2026

He insists that his focus is “the war inside Islam” between radicals and Western-aligned Muslim leaders.

From Salon ● Apr. 22, 2026

“I think extremists and the radicals are always a little too much for me to handle.”

From The Wall Street Journal ● Apr. 11, 2026

Neylan originally opposed Sproul’s version of the oath, on the curious grounds that it would simply encourage its targets—the radicals assumed to be swarming over the university—to commit perjury.

From "Big Science" by Michael Hiltzik

Related Words

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