From Anglo-Norman 'havok' — originally a military command authorizing soldiers to plunder freely, punishable by death if given without authorization.
Widespread destruction; great confusion or disorder.
From Anglo-Norman 'havok,' from Old French 'havot' (plundering, pillaging). 'Cry havoc!' was a military command authorizing soldiers to plunder and loot — once given, troops could seize whatever they wanted. Shakespeare used it in Julius Caesar: 'Cry havoc and let slip the dogs