Definition of lights–out
1 : a command or signal for putting out lights
2 : a prescribed bedtime for persons living under discipline
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First Known Use of lights–out
1868
LIGHTS–OUT Defined for English Language Learners
lights-out
play
noun
Definition of lights–out for English Language Learners
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: a time when people (such as soldiers, prisoners, or students) are required to turn out the lights and go to bed
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