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English definition of “alert”

alert

adjective     /əˈlɜːt/ US  /-ˈlɝːt/
C1 quick to see, understand, and act in a particular situation: I'm not feeling very alert today - not enough sleep last night! A couple of alert readers posted comments on the website pointing out the mistake. Parents should be alert to sudden changes in children's behaviour.PerceptiveUsing the eyesIntelligenceReacting and responding alertness     /-nəs/ noun [U] Knowledge and awareness
(Definition of alert adjective from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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