Radical= what?

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radical
/ˈradɪk(ə)l/
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adjective
  1. 1.
    (especially of change or action) relating to or affecting the fundamental nature of something; far-reaching or thorough.
    “a radical overhaul of the existing regulatory framework”
    synonyms: thoroughgoingthoroughcompletetotalentireabsoluteuttercomprehensiveexhaustive, root-and-branch, sweepingfar-reachingwide-rangingextensiveprofounddrasticsevereseriousmajordesperatestringentviolentforcefulrigorousdraconian

    “radical reform is long overdue”
noun
  1. 1.
    a person who advocates thorough or complete political or social change, or a member of a political party or section of a party pursuing such aims.
    synonyms: revolutionaryprogressivereformerrevisionistMore

  2. 2.
    CHEMISTRY
    a group of atoms behaving as a unit in a number of compounds.