/ ˈhævək; NAmE / noun
[ U ] a situation in which there is a lot of damage, destruction or confusion :
The floods caused havoc throughout the area.
Continuing strikes are beginning to play havoc with the national economy.
These insects can wreak havoc on crops.
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WORD ORIGIN
late Middle English : from Anglo-Norman French havok , alteration of Old French havot , of unknown origin. The word was originally used in the phrase cry havoc ( Old French crier havot ) to give an army the order havoc , which was the signal for plundering.