Simple Definition of zero hour
: the time at which an event (such as a military attack) is scheduled to begin
Full Definition of zero hour
1 a : the hour at which a planned military operation is scheduled to start b : 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
Examples of zero hour
<we're at the zero hour, so someone has to make a decision>
Origin of zero hour
from its being marked by the count of zero in a countdown
First Known Use: 1915
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Thesaurus: All synonyms and antonyms for "zero hour"
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