radical

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.

Definitions of radical
  1. adjective
    (used of opinions and actions) far beyond the norm
    radical opinions on education”
    synonyms: extremist, ultra
    immoderate
    beyond reasonable limits
  2. adjective
    markedly new or introducing radical change
    radical political views”
    synonyms: revolutionary
    new
    not of long duration; having just (or relatively recently) come into being or been made or acquired or discovered
  3. noun
    a person who has radical ideas or opinions
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    types:
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    anarchist, nihilist, syndicalist
    an advocate of anarchism
    Bolshevik, Marxist, bolshie, bolshy, red
    emotionally charged terms used to refer to extreme radicals or revolutionaries
    extremist
    a person who holds extreme views
    leveler, leveller
    a radical who advocates the abolition of social distinctions
    revolutionary, revolutionist, subversive, subverter
    a radical supporter of political or social revolution
    terrorist
    a radical who employs terror as a political weapon; usually organizes with other terrorists in small cells; often uses religion as a cover for terrorist activities
    Trot, Trotskyist, Trotskyite
    radicals who support Trotsky's theory that socialism must be established throughout the world by continuing revolution
    Wobbly
    a member of the Industrial Workers of the World
    young Turk
    a young radical who agitates for reform
    counter-revolutionist, counterrevolutionary, counterrevolutionist
    a revolutionary whose aim is to reverse the changes introduced by an earlier revolution
    dynamiter, dynamitist
    a person who uses dynamite in a revolutionary cause
    Girondin, Girondist
    a member of the moderate republican party that was in power during the French Revolution; the Girondists were overthrown by their more radical rivals the Jacobins
    cyber-terrorist, cyberpunk, hacker
    a programmer who breaks into computer systems in order to steal or change or destroy information as a form of cyber-terrorism
    freedom fighter, insurgent, insurrectionist, rebel
    a person who takes part in an armed rebellion against the constituted authority (especially in the hope of improving conditions)
    Jacobin
    a member of the radical movement that instituted the Reign of Terror during the French Revolution
    sleeper
    a spy or saboteur or terrorist planted in an enemy country who lives there as a law-abiding citizen until activated by a prearranged signal
    suicide bomber
    a terrorist who blows himself up in order to kill or injure other people
    type of:
    individual, mortal, person, somebody, someone, soul
    a human being
  4. noun
    a character conveying the lexical meaning of a logogram
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    type of:
    character, grapheme, graphic symbol
    a written symbol that is used to represent speech
  5. noun
    (linguistics) the form of a word after all affixes are removed
    synonyms: base, root, root word, stem, theme
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    type of:
    descriptor, form, signifier, word form
    the phonological or orthographic sound or appearance of a word that can be used to describe or identify something
  6. adjective
    of or relating to or constituting a linguistic root
    “a radical verb form”
  7. noun
    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
    synonyms: free radical
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    type of:
    atom
    (physics and chemistry) the smallest component of an element having the chemical properties of the element
  8. noun
    (chemistry) two or more atoms bound together as a single unit and forming part of a molecule
    synonyms: chemical group, group
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    types:
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    acyl, acyl group
    any group or radical of the form RCO- where R is an organic group
    alcohol group, alcohol radical
    the chemical group -OH
    aldehyde group, aldehyde radical
    the chemical group -CHO
    alkyl, alkyl group, alkyl radical
    any of a series of univalent groups of the general formula CnH2n+1 derived from aliphatic hydrocarbons
    allyl, allyl group, allyl radical
    the univalent unsaturated organic radical C3H5; derived from propylene
    amino, amino group
    the radical -NH2
    amyl
    a hydrocarbon radical that occurs in many organic compounds
    azido group, azido radical
    the univalent group N3- derived from hydrazoic acid
    azo group, azo radical
    the bivalent group -N=N- united to two hydrocarbon groups
    benzyl, benzyl group, benzyl radical
    the univalent radical derived from toluene
    benzoyl group, benzoyl radical
    the univalent radical derived from benzoic acid
    arsenic group, cacodyl, cacodyl group, cacodyl radical
    the univalent group derived from arsine
    carbonyl group
    the bivalent radical CO
    carboxyl, carboxyl group
    the univalent radical -COOH; present in and characteristic of organic acids
    chromophore
    the chemical group that gives color to a molecule
    cyanide group, cyanide radical, cyano group, cyano radical
    the monovalent group -CN in a chemical compound
    glyceryl
    a trivalent radical derived from glycerol by removing the three hydroxyl radicals
    hydrazo group, hydrazo radical
    the bivalent group -HNNH- derived from hydrazine
    hydroxyl, hydroxyl group, hydroxyl radical
    the monovalent group -OH in such compounds as bases and some acids and alcohols
    ketone group
    a group having the characteristic properties of ketones
    methylene, methylene group, methylene radical
    the bivalent radical CH2 derived from methane
    propyl, propyl group, propyl radical
    the monovalent organic group C3H7- obtained from propane
    butyl
    a hydrocarbon radical (C4H9)
    nitro group
    the group -NO3
    nitrite
    the radical -NO2 or any compound containing it (such as a salt or ester of nitrous acid)
    uranyl, uranyl group, uranyl radical
    the bivalent radical UO2 which forms salts with acids
    vinyl, vinyl group, vinyl radical
    a univalent chemical radical derived from ethylene
    acetyl, acetyl group, acetyl radical, ethanoyl group, ethanoyl radical
    the organic group of acetic acid (CH3CO-)
    ethyl, ethyl group, ethyl radical
    the univalent hydrocarbon radical C2H5 derived from ethane by the removal of one hydrogen atom
    glucosamine
    an amino derivative of glucose that is a component of many polysaccharides
    foryml
    (chemistry) the negative univalent acyl radical CHO that occurs in aldehydes
    methyl, methyl group, methyl radical
    the univalent radical CH3- derived from methane
    sodium nitrite
    nitrite used to preserve and color food especially in meat and fish products; implicated in the formation of suspected carcinogens
    type of:
    building block, unit
    a single undivided natural thing occurring in the composition of something else
  9. noun
    (mathematics) a quantity expressed as the root of another quantity
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    type of:
    amount, measure, quantity
    how much there is or how many there are of something that you can quantify
  10. adjective
    arising from or going to the root or source
    “a radical flaw in the plan”
    Synonyms:
    basic
    pertaining to or constituting a base or basis
  11. adjective
    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
    radical leaves”
    synonyms: basal
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    Antonyms:
    cauline
    especially of leaves; growing on a stem especially on the upper part of a stem
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