havoc (n.)

early 15c., from the expression cry havoc "give the signal to pillage" (Anglo-French crier havok, late 14c.). Havok, the signal to soldiers to seize plunder, is from Old French havot "pillaging, looting" (in crier havot), which is related to haver "to seize, grasp," hef "hook," probably from a Germanic source (see hawk (n.)), or from Latin habere "to have, possess." General sense of "devastation" first recorded late 15c.