zero hour
noun
Definition of zero hour
1a : the hour at which a planned military operation is scheduled to startb : the time at which a usually significant or notable event is scheduled to take place
2 : a time when a vital decision or decisive change must be made
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Examples of zero hour in a Sentence
we're at the zero hour, so someone has to make a decision
Origin and Etymology of zero hour
from its being marked by the count of zero in a countdown
First Known Use: 1915
ZERO HOUR Defined for English Language Learners
zero hour
noun
Definition of zero hour for English Language Learners
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: the time at which an event (such as a military attack) is scheduled to begin
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