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English definition of “insanity”

insanity

noun [U]     /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.Of unsound mindStupid and silly an action that is stupid and likely to have extremely bad results: It would be insanity to expand the business now.Stupid and sillyOf unsound mind
(Definition of insanity noun from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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