• WordNet 3.6
    • adj radical especially of leaves; located at the base of a plant or stem; especially arising directly from the root or rootstock or a root-like stem "basal placentation","radical leaves"
    • adj radical (used of opinions and actions) far beyond the norm "extremist political views","radical opinions on education","an ultra conservative"
    • adj radical markedly new or introducing radical change "a revolutionary discovery","radical political views"
    • adj radical arising from or going to the root or source "a radical flaw in the plan"
    • adj radical of or relating to or constituting a linguistic root "a radical verb form"
    • n radical (linguistics) the form of a word after all affixes are removed "thematic vowels are part of the stem"
    • n radical a character conveying the lexical meaning of a logogram
    • n radical a person who has radical ideas or opinions
    • n radical (mathematics) a quantity expressed as the root of another quantity
    • n radical (chemistry) two or more atoms bound together as a single unit and forming part of a molecule
    • n radical an atom or group of atoms with at least one unpaired electron; in the body it is usually an oxygen molecule that has lost an electron and will stabilize itself by stealing an electron from a nearby molecule "in the body free radicals are high-energy particles that ricochet wildly and damage cells"
    • ***
Webster's Revised Unabridged Dictionary
    • Radical (Chem) A characteristic, essential, and fundamental constituent of any compound; hence, sometimes, an atom.
    • Radical (Philol) A primitive letter; a letter that belongs to the radix.
    • Radical (Philol) A primitive word; a radix, root, or simple, underived, uncompounded word; an etymon.
    • Radical (Alg) A radical quantity. See under Radical a. "An indicated root of a perfect power of the degree indicated is not a radical but a rational quantity under a radical form."
    • Radical (Anat) A radical vessel. See under Radical a.
    • Radical (Bot) Belonging to, or proceeding from, the root of a plant; as, radical tubers or hairs.
    • Radical Hence: Of or pertaining to the root or origin; reaching to the center, to the foundation, to the ultimate sources, to the principles, or the like; original; fundamental; thorough-going; unsparing; extreme; as, radical evils; radical reform; a radical party. "The most determined exertions of that authority, against them, only showed their radical independence."
    • Radical (Math) Of or pertaining to a radix or root; as, a radical quantity; a radical sign. See below.
    • Radical Of or pertaining to the root; proceeding directly from the root.
    • Radical (Politics) One who advocates radical changes in government or social institutions, especially such changes as are intended to level class inequalities; -- opposed to conservative. "In politics they [the Independents] were, to use the phrase of their own time, “Root-and-Branch men,” or, to use the kindred phrase of our own, Radicals ."
    • Radical (Bot) Proceeding from a rootlike stem, or one which does not rise above the ground; as, the radical leaves of the dandelion and the sidesaddle flower.
    • Radical (Philol) Relating, or belonging, to the root, or ultimate source of derivation; as, a radical verbal form.
    • Radical (Chem) Specifically, a group of two or more atoms, not completely saturated, which are so linked that their union implies certain properties, and are conveniently regarded as playing the part of a single atom; a residue; -- called also a compound radical. Cf. Residue.
    • ***
Century Dictionary and Cyclopedia
    • radical Pertaining or relating to a root or to roots.
    • radical Specifically— In botany, belonging to the root: opposed to cauline. See radical leaves and radical peduncle, below.
    • radical In philology, of the nature of or pertaining to a root, or a primary or underived word or main part of a word: as, a radical word; a radical letter or syllable; radical accentuation.
    • radical In mathematics, consisting of or indicating one of the roots of a number: as, a radical expression; the radical sign.
    • radical In chem., noting any atom or group of atoms which is, for the moment, regarded as a chief constituent of the molecules of a given compound, and which does not lose its integrity in the ordinary chemical reactions to which the substance is liable.
    • radical Making part of the essential nature of the subject or thing concerned; existing inherently; intrinsic; organic: as, radical defects of character; a radical fault of construction; the radical principles of an art or of religion. The Latin word first occurs, about the beginning of the thirteenth century, in the phrase humidum radicale, or radical moisture, that moisture in an animal or a plant which cannot be expelled without killing the organism which was supposed to remain unchanged throughout life, and to be the chief principle of vitality. The word seems to translate the pseudo-Aristotelian ως ἄν ει%148ποι τις ῤίζαι ‘as one may say, roots’—an expression applied to moisture and certain other conditions as being essential to the life of plants.
    • radical Of or pertaining to the root or foundation of the subject; concerned with or based upon fundamental principles; hence, thoroughgoing; extreme: as, a radical truth; a radical difference of opinion; radical views or measures; the Radical party in British politics.
    • radical Of or pertaining to a political party or body of persons known as Radicals (see II., 4, below): as, a Radical candidate; the Radical program.
    • radical Synonyms There may be a distinction between a radical reform, change, cure, or the like, and one that is thorough, entire, complete, or thoroughgoing, radical emphasizing only the fact of going to the root, whether there is thoroughness or entireness or not. Yet that which is radical is likely to be thorough, etc.
    • n radical In philology:
    • n radical A radical word or part of a word; especially, a primitive word or verbal element serving as a root of inflected or derivative words.
    • n radical A radical letter; a letter forming an essential part of the primitive form or root of a word. Also radicle.
    • n radical In chem., an element or group of combined elements which remains after one or more elements have been removed from a compound. (See the quotation.) The term is chiefly applied to compound radicals, which are assumed to exist in compound bodies and to remain intact in many of the chemical changes which these bodies undergo. Thus the compound radical ethyl, C2H5, appears in alcohol (C2H5.OH), in ether ((C2H5)2O), in ethylamine (C2H5.NH2), etc., and may be transferred without change, like an element, from one of these compounds to the other. Also radicle.
    • n radical In music, same as root.
    • n radical A person who holds or acts according to radical principles; one who pursues a theory to its furthest apparent limit; an extremist, especially in politics. In the political sense, in which the word has been most used, a Radical is one who aims at thorough reform in government from a liberal or democratic point of view, or desires the establishment of what he regards as abstract principles of right and justice, by the most direct and uncompromising methods. The political Radicals of a country generally constitute the extreme faction or wing of the more liberal of the two leading parties, or act as a separate party when their numbers are sufficient for the exertion of any considerable influence. The name Radical is often applied as one of reproach to the members of a party by their opponents. In the United States it has been so applied at times to Democrats, and to Republicans especially in the South about the period of reconstruction. The French Radicals are often called the Extreme Left. The British Radicals form an important section of the Liberal party.
    • n radical In algebra, a quantity expressed as a root of another quantity.
    • n radical See the adjectives.
    • radical In astrology, belonging to the radix or original scheme of nativity; in horary astrology, ripe and proper for judgment.
    • n radical A minute vessel which unites with others to form a large branch or trunk. See radicle, 2.
    • n radical In England, the name given to a white hat which was formerly somewhat worn by Radicals, owing to the fact that Henry Hunt [a radical English politician, 1773–1835] wore a white hat at various political gatherings in 1820.
    • ***
Chambers's Twentieth Century Dictionary
    • adj Radical rad′i-kal pertaining to the root or origin: original: fundamental: intrinsic: primitive: implanted by nature: not derived: serving to originate: :
    • n Radical a root: a primitive word or letter: one who advocates radical reform, an uncompromising democratic politician:
    • v.i Radical to become radical, adopt radical political principles
    • adj Radical rad′i-kal (bot.) proceeding immediately from the root
    • adj Radical rad′i-kal (politics) ultra-liberal, democratic
    • n Radical (chem.) the base of a compound
    • ***


  • Walter Lippmann
    “Our conscience is not the vessel of eternal verities. It grows with our social life, and a new social condition means a radical change in conscience.”
  • Mark Twain
    “The radical invents the views. When he has worn them out, the conservative adopts them.”
  • Alice Walker
    “The gift of loneliness is sometimes a radical vision of society or one's people that has not previously been taken into account.”
  • John Fischer
    John Fischer
    “What this country needs is radicals who will stay that way regardless of the creeping years.”
  • Franklin D. Roosevelt
    “A radical is a man with both feet firmly planted in the air.”
  • Oscar Wilde
    “He thinks like a Tory, and talks like a Radical, and that's so important nowadays.”


Webster's Revised Unabridged Dictionary
F., fr. L. radicalis, having roots, fr. radix, -icis, a root. See Radix


In literature:

This stultification of principle, of radical public sentiment, stirred the soul of Miss Dickinson, and she desired to speak.
"History of Woman Suffrage, Volume II"
I am utterly and radically opposed to it.
"A Romantic Young Lady" by Robert Grant
Regarding the family equipment, the situation in the city is certainly radically different from what it was.
"Rural Problems of Today" by Ernest R. Groves
Carl Doerflinger read a greeting in behalf of the German Radicals of the city.
"History of Woman Suffrage, Volume III (of III)" by Various
We cannot form a real alliance with thinkers radically opposed to us.
"Social Rights and Duties, Volume I (of 2)" by Sir Leslie Stephen
The radical and the puritanic elements in the Republican party were terribly scared.
"Diary from March 4, 1861, to November 12, 1862" by Adam Gurowski
Surely there is something radically wrong in this attitude.
"Jennie Gerhardt" by Theodore Dreiser
The radicals wanted a clear-cut democracy.
"The Story of the Great War, Volume VI (of VIII)" by Various
In the discussion of these ideals and this social philosophy, we hear much of radicalism and of reaction.
"Herbert Hoover" by Vernon Kellogg
For in his growth as a radical, Joe had gone beyond all arguing now.
"The Harbor" by Ernest Poole

In poetry:

I think that Samuel Johnson said
His side had won the day,
Had not we women radicals
Just got right in the way.
"The Deliverance" by Frances Ellen Watkins
Then, in the future that we see,
Bamford, the Radical, shall live anew,
And be proclaim'd abroad, as he
Who fought for Freedom when her friends were few!
"Lines, to Mr. Samuel Bamford, on his seventy-sixth birthday, February 28th, 1864." by Samuel Bamford
So I turn tory for the nonce,
And think the radical a bore,
Who cannot see, thick-witted dunce,
That what was good for people once
Must be as good forevermore.
"The Optimist" by James Russell Lowell

In news:

As the top Republican on the Senate Committee on Environment and Public Works, I have worked every day to expose the radical left'...
The Romney Budget is Even More Radical Than the Ryan Budget.
He has a new girl, a radical Y.W.C.A.
D aniel McGowan was the son of a Rockaways cop, but he made a name for himself as a radical.
Metro in the process of installing a series pro-Israel ads across the transit system Monday that equates Muslim radicals with savages.
But Eta 's high command is said to have passed into the hands of younger, more radical leaders who forced the breaking of the ceasefire.
LONDON — Radical Muslim cleric Abu Hamza al-Masri has lost a court appeal to block extradition to the US to face terrorism charges that include trying to set up an al Qaeda training camp in rural Oregon.
Fabled Resort's Restaurant Radically New.
Is Nicky Oppenheimer an old-fashioned mining tycoon or a radical economic reformer.
In Pakistan, educated middle-class youths such as Faisal Shahzad, the accused Times Square car bomber, have ready access to jihadist and other radical, anti-American resources.
How radically the world has changed.
Why Indonesia's Islamist radicals attack.
Adams wasn't a big fan of Paine–envying his fame while worrying about his radical democratic ideals.
Gennady Gudkov is the last person you'd think of as a radical dissident.
Nobel laureate Wole Soyinka on Friday dismissed calls for peace negotiations with the radical Islamist sect known as Boko Haram and said Nigerian society is at stake in what he described as a war for survival.

In science:

In Section 7.2 we compute the radical and semisimple quotient of the semigroup algebra.
Semigroups, rings, and Markov chains
One can express the first sentence of Theorem 3 by saying that J is the radical of the ring kS and that kL is the semisimple quotient.
Semigroups, rings, and Markov chains
Suppose further that P is a parabolic subgroup of G with abelian unipotent radical (with aura).
Moore-Penrose inverse, parabolic subgroups, and Jordan pairs
Here p = g0 ⊕ g1 is a Lie algebra of P and exp g1 is the abelian unipotent radical of P .
Moore-Penrose inverse, parabolic subgroups, and Jordan pairs
By Pyasetsky theorem [P] this holds if and only if P has finitely many orbits in the dual module (g/p)∗ , or, equivalently, in the unipotent radical of P .
Moore-Penrose inverse, parabolic subgroups, and Jordan pairs