alert in WordNet English dictionary

1. an automatic signal (usually a sound) warning of danger
   alarm  alert  warning signal  alarum 
   
2. a warning serves to make you more alert to danger
   alert  alerting 
   
3. condition of heightened watchfulness or preparation for action
   "bombers were put on alert during the crisis"
   alert  qui vive 
   

1. warn or arouse to a sense of danger or call to a state of preparedness
   "The empty house alarmed him"; "We alerted the new neighbors to the high rate of burglaries"
   alarm  alert 
   

1. engaged in or accustomed to close observation
   "caught by a couple of alert cops"; "alert enough to spot the opportunity when it came"; "constantly alert and vigilant, like a sentinel on duty"
   alert  watchful 
   
2. mentally perceptive and responsive;"an alert mind"
   "alert to the problems"; "alive to what is going on"; "awake to the dangers of her situation"; "was now awake to the reality of his predicament"
   alert  alive  awake 
   
3. quick and energetic
   "a brisk walk in the park"; "a lively gait"; "a merry chase"; "traveling at a rattling rate"; "a snappy pace"; "a spanking breeze"
   alert  brisk  lively  merry  rattling  snappy  spanking  zippy