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1. The process of paying close and continuous attention
   "wakefulness, alertness, and bellicosity make a good hunter";
   - watchfulness, wakefulness, vigilance
    
2. A state of readiness to respond
   "alertness was indicated by the desynchronization of the EEG";
   - alerting
    
3. Lively attentiveness
   - sharp-sightedness, on the qui vive

Type of: arousal, attention, attentiveness

Encyclopedia: Alertness