American English

Definition of lockdown noun from the Oxford Advanced American Dictionary

 

lockdown

 noun
noun
NAmE//ˈlɑkdaʊn//
 
[countable, uncountable]
 
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an official order to control the movement of people or vehicles because of a dangerous situation a three-day lockdown of American airspace Prisoners have been placed on lockdown to prevent further violence at the jail. The prison warden ordered an instant lockdown = prisoners were locked in their cells. The city schools were in lockdown.
See the Oxford Advanced Learner's Dictionary entry: lockdown