Definition of alertness noun from the Oxford Advanced Learner's Dictionary



    BrE BrE//əˈlɜːtnəs//
    ; NAmE NAmE//əˈlɜːrtnəs//
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  1. 1the ability to think quickly and to notice things Sleep deprivation could affect mental alertness.
  2. 2great awareness of something, especially a problem or danger With a real threat of ambush, the crews remained at a high state of alertness.