[ rad-i-kuhl ]
See synonyms for radical on Thesaurus.com
  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.

  2. extreme, especially as regards change from accepted or traditional forms: a radical change in the policy of the company.

  1. favoring drastic political, economic, or social reforms: radical ideas;radical and anarchistic ideologues.

  2. favoring, supporting, or representing extreme forms of religious fundamentalism: radical fundamentalists and their rejection of modern science.

  3. forming a basis or foundation: What is the radical reason for his choice?

  4. existing inherently in a thing or person: radical defects of character.

  5. 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.

  6. Slang. excellent; wonderful; cool; rad: You got here on an electric skateboard? That's radical!

  7. Mathematics.

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

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

  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.

  1. Mathematics.

    • a quantity expressed as a root of another quantity.

    • the set of elements of a ring, some power of which is contained in a given ideal.

  2. Chemistry.

  3. Grammar. root1 (def. 12).

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

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 -al1;see also root1

synonym study For radical

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, 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.

word story For radical

Radical comes straight from the Late Latin adjective rādicālis “having roots, rooted,” first occurring about a.d. 400 in Contra Faustum (“Against Faustus the Manichaean”) by St. Augustine of Hippo. Rādicālis is a derivative of the noun rādix (inflectional stem rādīc- ) “root (of a plant, tooth, hair), root (of a family, stock, breed), (etymological) root.” The mathematical sense “denoting the radical sign which indicates the root of a number” dates from the late 17th century. Radical in its political sense dates from the late 18th century in England and the first half of the 19th century in the United States.
Latin rādix comes from wrād-, one of the variants of the Proto-Indo-European root wrād, werād, wred- “root, branch.” From this same variant, Latin also has rāmus “branch” (the root, so to speak, of English ramify ), while Greek has rhádix (stem rhádik- ). Another variant of the root is the possible source of Greek rhiza, source of English rhizome; other variants include Aeolic briza, brisda and Mycenaean wriza. Wrād- regularly becomes wrōt- in Proto-Germanic, the ultimate source of the English word root.

Other words for radical

Opposites for radical

Other words from radical

  • rad·i·cal·i·ty [rad-i-kal-i-tee], /ˌræd ɪˈkæl ɪ ti/, rad·i·cal·ness, noun
  • mul·ti·rad·i·cal, adjective
  • non·rad·i·cal, adjective, noun
  • qua·si-rad·i·cal, adjective
  • sem·i·rad·i·cal, adjective
  • sub·rad·i·cal, adjective
  • su·per·rad·i·cal, adjective
  • ul·tra·rad·i·cal, adjective, noun
  • un·rad·i·cal, adjective

Words Nearby radical

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use radical in a sentence

British Dictionary definitions for radical


/ (ˈrædɪkəl) /

  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

  1. favouring or tending to produce extreme or fundamental changes in political, economic, or social conditions, institutions, habits of mind, etc: a radical party

  2. med (of treatment) aimed at removing the source of a disease: radical surgery

  3. slang, mainly US very good; excellent

  4. of, relating to, or arising from the root or the base of the stem of a plant: radical leaves

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

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

  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

  1. Also: radicle chem

  2. linguistics another word for root 1 (def. 9)

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

Origin of radical

C14: from Late Latin rādīcālis having roots, from Latin rādix a root

Derived forms of radical

  • radicalness, noun

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

Scientific definitions for radical


[ rădĭ-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.

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

Cultural definitions for radical (1 of 2)


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


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

Notes for radical

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

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.