A warning that is given about something that fails to occur.

Roget 669: alarm; alarum, larum^†, alarm bell, tocsin, alerts, beat of drum, sound of trumpet, note of alarm, hue and cry, fire cross, signal of distress; blue lights; war-cry, war-whoop; warning etc. 668; fogsignal, foghorn; yellow flag; danger signal; red light, red flag; fire bell; police whistle.    false alarm, cry of wolf; bug-bear, bugaboo.    ... meer laten zien