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English definition of “radical”

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radical

adjective uk   /ˈræd.ɪ.kəl/ us  

radical adjective (SUPPORTING CHANGE)

C2 believing or expressing the belief that there should be great or extreme social or political change: He was known as a radical reformer/thinker/politician. These people have very radical views.
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radical adjective (VERY IMPORTANT)

C1 relating to the most important parts of something or someone; complete or extreme: We need to make some radical changes to our operating procedures. She has had to undergo radical surgery (= aimed at removing the cause of a disease).
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radical adjective (extensive)

specialized medical aimed at removing all diseased tissue: Cervical cancer may be cured with radical surgery when it is confined to the pelvis or regional lymph nodes.
radically
adverb uk   /-i/ us  
C1 Barker introduced some radically new ideas.

radical

noun [C] uk   /ˈræd.ɪ.kəl/ us  
C2 a person who supports great social and political change: She was a radical all her life.
radicalism
noun [U] uk   /-ɪ.zəm/ us  
(Definition of radical from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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