Definitions by Collins English Electronic Dictionary Digital Edition: 2008 © HarperCollins Publishers 2008

1. alert

   1. adjective, vigilantly attentive
   2. adjective, brisk, nimble, or lively
   3. noun, an alarm or warning, esp a siren warning of an air raid
   4. noun, the period during which such a warning remains in effect
   5. noun, on the alert a) on guard against danger, attack, etc b) watchful; ready
   6. verb, to warn or signal (troops, police, etc) to prepare for action
   7. verb, to warn of danger, an attack, etc
   8. Show me some examples of this word: alert

By Defined by Harper Collins