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English definition of “alert”

alert

adjective     /əˈlɜːt/
quick to notice and react to things around you: A young dog should be alert and playful. Teachers need to be alert to sudden changes in students' behaviour.PerceptiveUsing the eyesIntelligence
alertness noun [U]
(Definition of alert adjective from the Cambridge Learner's Dictionary © Cambridge University Press)

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