1.  radical(n = noun.substance) chemical group, group - (chemistry) two or more atoms bound together as a single unit and forming part of a molecule;
is a kind of building block, unit
is a part of molecule
has particulars: acyl, acyl group, alcohol group, alcohol radical, aldehyde group, aldehyde radical, alkyl, alkyl group, alkyl radical, allyl, allyl group, allyl radical, amino, amino group, amyl, azido group, azido radical, azo group, azo radical, benzyl, benzyl group, benzyl radical, benzoyl group, benzoyl radical, arsenic group, cacodyl, cacodyl group, cacodyl radical, carbonyl group, carboxyl, carboxyl group, chromophore, cyanide group, cyanide radical, cyano group, cyano radical, glyceryl, hydrazo group, hydrazo radical, hydroxyl, hydroxyl group, hydroxyl radical, ketone group, methylene, methylene group, methylene radical, propyl, propyl group, propyl radical, butyl, nitro group, nitrite, uranyl, uranyl group, uranyl radical, vinyl, vinyl group, vinyl radical

2.  radical(n = noun.substance) free 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"
is a kind of atom

3.  radical(n = noun.person) - a person who has radical ideas or opinions;
is a kind of individual, mortal, person, somebody, someone, soul
has particulars: anarchist, nihilist, syndicalist, bolshevik, bolshie, bolshy, marxist, red, extremist, leveler, leveller, revolutionary, revolutionist, subversive, subverter, terrorist, trot, trotskyist, trotskyite, wobbly, young turk

4.  radical(n = noun.quantity) - (mathematics) a quantity expressed as the root of another quantity;
is a kind of amount, measure, quantity

5.  radical(n = noun.communication) - a character conveying the lexical meaning of a logogram;
is a kind of character, grapheme, graphic symbol
is a part of ideogram, ideograph

6.  radical(n = noun.communication) base, root, root word, stem, theme - (linguistics) the form of a word after all affixes are removed; "thematic vowels are part of the stem"
is a kind of descriptor, form, signifier, word form

1.  radical(s = adj.all) extremist, ultra - (used of opinions and actions) far beyond the norm; "extremist political views"; "radical opinions on education"; "an ultra conservative"

2.  radical(s = adj.all) revolutionary - markedly new or introducing radical change; "a revolutionary discovery"; "radical political views"

3.  radical(s = adj.all) - arising from or going to the root or source; "a radical flaw in the plan"

4.  radical(a = adj.pert) - of or relating to or constituting a linguistic root; "a radical verb form"

5.  radical(a = adj.all) basal - 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"
Antonym: cauline

1.  Of or pertaining to the root; proceeding directly from the root. [1913 Webster]

2.  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. [1913 Webster]
"The most determined exertions of that authority, against them, only showed their radical independence." [1913 Webster]

3.  Belonging to, or proceeding from, the root of a plant; as, radical tubers or hairs. [1913 Webster]

4.  Relating, or belonging, to the root, or ultimate source of derivation; as, a radical verbal form. [1913 Webster]

5.  Of or pertaining to a radix or root; as, a radical quantity; a radical sign. See below. [1913 Webster]

1.  A primitive word; a radix, root, or simple, underived, uncompounded word; an etymon. [1913 Webster]
"The words we at present make use of, and understand only by common agreement, assume a new air and life in the understanding, when you trace them to their radicals, where you find every word strongly stamped with nature; full of energy, meaning, character, painting, and poetry." [1913 Webster]

2.  One who advocates radical changes in government or social institutions, especially such changes as are intended to level class inequalities; -- opposed to conservative. [1913 Webster]
"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." [1913 Webster]

3.  A characteristic, essential, and fundamental constituent of any compound; hence, sometimes, an atom. [1913 Webster]
"As a general rule, the metallic atoms are basic radicals, while the nonmetallic atoms are acid radicals." [1913 Webster]

4.  A radical quantity. See under Radical, a. [1913 Webster]
"An indicated root of a perfect power of the degree indicated is not a radical but a rational quantity under a radical form." [1913 Webster]

5.  A radical vessel. See under Radical, a. [1913 Webster]

radical, adj. & n.
--adj.
1 of the root or roots; fundamental (a radical error).
2 far-reaching; thorough; going to the root (radical change).
3 a advocating thorough reform; holding extreme political views; revolutionary. b (of a measure etc.) advanced by or according to principles of this kind.
4 forming the basis; primary (the radical idea).
5 Math. of the root of a number or quantity.
6 (of surgery etc.) seeking to ensure the removal of all diseased tissue.
7 of the roots of words.
8 Mus. belonging to the root of a chord.
9 Bot. of, or springing direct from, the root.
10 hist. belonging to an extreme section of the Liberal party.
11 US hist. seeking extreme anti-South action at the time of the Civil War.
--n.
1 a person holding radical views or belonging to a radical party.
2 Chem. a a free radical. b an element or atom or a group of these normally forming part of a compound and remaining unaltered during the compound's ordinary chemical changes.
3 the root of a word.
4 a fundamental principle; a basis.
5 Math. a a quantity forming or expressed as the root of another. b a radical sign.

Idiom:
radical sign indicating the square, cube, etc., root of the number following.

Derivative:
radicalism n. radicalize v.tr. & intr. (also -ise). radicalization n. radically adv. radicalness n.

Etymology:
ME f. LL radicalis f. L radix radicis root

N  intrinsicality, inbeing, inherence, inhesion, subjectiveness, ego, egohood, essence, noumenon, essentialness, essential part, quintessence, incarnation, quiddity, gist, pith, marrow, core, sap, lifeblood, backbone, heart, soul, important part, principle, nature, constitution, character, type, quality, crasis, diathesis, habit, temper, temperament, spirit, humor, grain, disposition, endowment, capacity, capability, moods, declensions, features, aspects, peculiarities, idiosyncrasy, oddity, idiocrasy, diagnostics, derived from within, subjective, intrinsic, intrinsical, fundamental, normal, implanted, inherent, essential, natural, innate, inborn, inbred, ingrained, inwrought, coeval with birth, genetous, haematobious, syngenic, radical, incarnate, thoroughbred, hereditary, inherited, immanent, congenital, congenite, connate, running in the blood, ingenerate, ingenite, indigenous, in the grain, bred in the bone, instinctive, inward, internal, to the manner born, virtual, characteristic, invariable, incurable, incorrigible, ineradicable, fixed, intrinsically, at bottom, in the main, in effect, practically, virtually, substantially, au fond, fairly, character is higher than intellect, come give us a taste of your quality, magnos homines virtute metimur non fortuna, non numero haec judicantur sed pondere, vital spark of heavenly flame.

N  importance, consequence, moment, prominence, consideration, mark, materialness, import, significance, concern, emphasis, interest, greatness, superiority, notability, weight, value, usefulness, gravity, seriousness, solemnity, no joke, no laughing matter, pressure, urgency, stress, matter of life and death, memorabilia, notabilia, great doings, red-letter day, great thing, great point, main chance, the be all and the end all, cardinal point, substance, gist, sum and substance, gravamen, head and front, important part, principal part, prominent part, essential part, half the battle, sine qua non, breath of one's nostrils, cream, salt, core, kernel, heart, nucleus, keynote, keystone, corner stone, trump card, salient points, top sawyer, first fiddle, prima donna, chief, triton among the minnows, 'it', important, of importance, momentous, material, to the point, not to be overlooked, not to be despised, not to be sneezed at, egregious, weighty, of note, notable, prominent, salient, signal, memorable, remarkable, unforgettable, worthy of remark, worthy of notice, never to be forgotten, stirring, eventful, grave, serious, earnest, noble, grand, solemn, impressive, commanding, imposing, urgent, pressing, critical, instant, paramount, essential, vital, all-absorbing, radical, cardinal, chief, main, prime, primary, principal, leading, capital, foremost, overruling, of vital importance in the front rank, first-rate, superior, considerable, marked, rare, significant, telling, trenchant, emphatic, pregnant, tanti, materially, in the main, above all, kat' exochin, par excellence, to crown all, to beat all, expende Hannibalem!.

N  improvement, amelioration, melioration, betterment, mend, amendment, emendation, mending, advancement, advance, ascent, promotion, preferment, elevation, increase, cultivation, civilization, culture, march of intellect, menticulture, race-culture, eugenics, reform, reformation, revision, radical reform, second thoughts, correction, limoe labor, refinement, elaboration, purification, oxidation, repair, recovery, revise, new edition, reformer, radical, improving, progressive, improved, better, better off, better for, all the better for, better advised, reformatory, emendatory, reparatory, remedial, corrigible, improvable, accultural, on consideration, on reconsideration, on second thoughts, on better advice, ad melius inquirendum, urbent latericiam invenit marmoream reliquit.

N  completeness, completion, integration, allness, entirety, perfection, solidity, solidarity, unity, all, ne plus ultra, ideal, limit, complement, supplement, make-weight, filling, up, impletion, saturation, saturity, high water, high tide, flood tide, spring tide, fill, load, bumper, bellyful, brimmer, sufficiency, complete, entire, whole, perfect, full, good, absolute, thorough, plenary, solid, undivided, with all its parts, all- sided, exhaustive, radical, sweeping, thorough-going, dead, regular, consummate, unmitigated, sheer, unqualified, unconditional, free, abundant, brimming, brimful, topful, topfull, chock full, choke full, as full as an egg is of meat, as full as a vetch, saturated, crammed, replete, fraught, laden, full-laden, full-fraught, full-charged, heavy laden, completing, supplemental, supplementary, ascititious, completely, altogether, outright, wholly, totally, in toto, quite, all out, over head and ears, effectually, for good and all, nicely, fully, through thick and thin, head and shoulders, neck and heel, neck and crop, in all respects, in every respect, at all points, out and out, to all intents and purposes, toto coelo, utterly, clean, clean as a whistle, to the full, to the utmost, to the backbone, hollow, stark, heart and soul, root and branch, down to the ground, to the top of one's bent, as far as possible, a outrance, throughout, from first to last, from beginning to end, from end to end, from one end to the other, from Dan to Beersheba, from head to foot, from top to toe, from top to bottom, de fond en comble, a fond, a capite ad calcem, ab ovo usque ad mala, fore and aft, every, whit, every inch, cap-a-pie, to the end of the chapter, up to the brim, up to the ears, up to the eyes, as a as can be, on all accounts, sous tous les rapports, with a vengeance, with a witness, falsus in uno falsus in omnibus, false in one thing, false in everything, omnem movere lapidem, una scopa nuova spazza bene.

N  number, symbol, numeral, figure, cipher, digit, integer, counter, round number, formula, function, series, sum, difference, complement, subtrahend, product, multiplicand, multiplier, multiplicator, coefficient, multiple, dividend, divisor, factor, quotient, submultiple, fraction, rational number, surd, irrational number, transcendental number, mixed number, complex number, complex conjugate, numerator, denominator, decimal, circulating decimal, repetend, common measure, aliquot part, prime number, prime, relative prime, prime factor, prime pair, reciprocal, totient, binary number, octal number, hexadecimal number, permutation, combination, variation, election, ratio, proportion, comparison, progression, arithmetical progression, geometrical progression, harmonical progression, percentage, permilage, figurate numbers, pyramidal numbers, polygonal numbers, power, root, exponent, index, logarithm, antilogarithm, modulus, base, differential, integral, fluxion, fluent, numeral, complementary, divisible, aliquot, reciprocal, prime, relatively prime, fractional, decimal, figurate, incommensurable, proportional, exponential, logarithmic, logometric, differential, fluxional, integral, totitive, positive, negative, rational, irrational, surd, radical, real, complex, imaginary, finite, infinite, impossible, numerically, modulo.

N  cause, origin, source, principle, element, occasioner, prime mover, primum mobile, vera causa, author, mainspring, agent, leaven, groundwork, foundation, spring, fountain, well, font, fountainhead, spring head, wellhead, fons et origo, genesis, descent, remote cause, influence, pivot, hinge, turning point, lever, crux, fulcrum, key, proximate cause, causa causans, straw that breaks the camel's back, ground, reason, reason why, why and wherefore, rationale, occasion, derivation, final cause, les dessous des cartes, undercurrents, rudiment, egg, germ, embryo, bud, root, radix radical, etymon, nucleus, seed, stem, stock, stirps, trunk, tap-root, gemmule, radicle, semen, sperm, nest, cradle, nursery, womb, nidus, birthplace, hotbed, causality, causation, origination, production, caused, causal, original, primary, primitive, primordial, aboriginal, protogenal, radical, embryonic, embryotic, in embryo, in ovo, seminal, germinal, at the bottom of, connate, having a common origin, because, behind the scenes, causa latet vis est notissima, felix qui potuit rerum cognoscere causas.

acetyl radical, alcohol radical, aldehyde radical, alkyl radical, allyl radical, azido radical, azo radical, benzoyl radical, benzyl radical, cacodyl radical, cyanide radical, cyano radical, ethanoyl radical, ethyl radical, free radical, hydrazo radical, hydroxyl radical, methyl radical, methylene radical, modified radical mastectomy, propyl radical, radical cell, radical chic, radical hysterectomy, radical mastectomy, radical right, radical sign, uranyl radical, vinyl radical