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English definition of “radical”

radical

adjective (VERY IMPORTANT)    /ˈræd.ɪ.kəl/
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).Very important or urgent radically     /-i/ adverb C1 Barker introduced some radically new ideas.Very important or urgent
(Definition of radical adjective (VERY IMPORTANT) from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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