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English definition of “insanity”

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insanity

noun [U] uk   /ɪnˈsæn.ə.ti/ us    /-t̬i/
the condition of being seriously mentally ill: He was found not guilty of murder by reason of insanity. He suffered from periodic bouts of insanity. an action that is stupid and likely to have extremely bad results: It would be insanity to expand the business now.
(Definition of insanity from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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