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English definition of “irrational”

irrational

adjective     /ɪˈræʃ.ən.əl/
C2 not using reason or clear thinking : It's totally irrational, but I'm frightened of mice . His parents were worried by his increasingly irrational behaviour .Of unsound mindStupid and silly irrationally     /-i/ adverb People often behave irrationally when they are under stress .Of unsound mindStupid and silly irrationality     /ɪˌræʃ.ənˈæl.ə.ti/ US  /-t̬i/ noun [U] Of unsound mindStupid and silly
(Definition of irrational adjective from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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