Definition of alert adjective from the Oxford Advanced Learner's Dictionary



    BrE BrE//əˈlɜːt//
    ; NAmE NAmE//əˈlɜːrt//
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  1. 1able to think quickly; quick to notice things Suddenly he found himself awake and fully alert. Two alert scientists spotted the mistake. Try to stay alert while driving at night. an alert mind mentally alert
  2. 2alert to something aware of something, especially a problem or danger We must be alert to the possibility of danger. She was alert to the slightest sound.
  3. Word Originlate 16th cent. (originally in military use): from French alerte, from Italian all' erta ‘to the watchtower’.Extra examples He was as mentally alert as a man half his age. The machine should help to keep the pilot alert. There was a noise outside and he was suddenly alert.
See the Oxford Advanced American Dictionary entry: alert