| Noun | 1. | air alert - the time period during which military and civilian agencies are prepared for an enemy air attackperiod, period of time, time period - an amount of time; "a time period of 30 years"; "hastened the period of time of his recovery"; "Picasso's blue period" | |
| 2. | air alert - the condition in which combat aircraft are airborne and ready for an operation; "aircraft in the Mideast are on air alert"alert, qui vive - condition of heightened watchfulness or preparation for action; "bombers were put on alert during the crisis" | |
| 3. | air alert - the warning signal that begins an period of preparation for an enemy air attack | |