zero hour

noun

Definition of zero hour

1a : 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

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Examples of zero hour in a Sentence

we're at the zero hour, so someone has to make a decision
Recent Examples on the Web Major milestones in the emergency plan are performed according to a predetermined schedule in the hours and days leading up to the zero hour. Daniel B. Hess, CNN, "How do hospitals prepare for hurricanes?," 2 Sep. 2019 Major milestones in the emergency plan are performed according to a predetermined schedule in the hours and days leading up to the zero hour. Daniel B. Hess, CNN, "How do hospitals prepare for hurricanes?," 2 Sep. 2019 Major milestones in the emergency plan are performed according to a predetermined schedule in the hours and days leading up to the zero hour. Daniel B. Hess, CNN, "How do hospitals prepare for hurricanes?," 2 Sep. 2019 Major milestones in the emergency plan are performed according to a predetermined schedule in the hours and days leading up to the zero hour. Daniel B. Hess, CNN, "How do hospitals prepare for hurricanes?," 2 Sep. 2019 Major milestones in the emergency plan are performed according to a predetermined schedule in the hours and days leading up to the zero hour. Daniel B. Hess, CNN, "How do hospitals prepare for hurricanes?," 2 Sep. 2019 Major milestones in the emergency plan are performed according to a predetermined schedule in the hours and days leading up to the zero hour. Daniel B. Hess, CNN, "How do hospitals prepare for hurricanes?," 2 Sep. 2019 Major milestones in the emergency plan are performed according to a predetermined schedule in the hours and days leading up to the zero hour. Daniel B. Hess, CNN, "How do hospitals prepare for hurricanes?," 2 Sep. 2019 Major milestones in the emergency plan are performed according to a predetermined schedule in the hours and days leading up to the zero hour. Daniel B. Hess, CNN, "How do hospitals prepare for hurricanes?," 2 Sep. 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'zero hour.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of zero hour

1915, in the meaning defined at sense 1a

History and Etymology for zero hour

from its being marked by the count of zero in a countdown

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Time Traveler for zero hour

Time Traveler

The first known use of zero hour was in 1915

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Statistics for zero hour

Last Updated

9 Jan 2020

Cite this Entry

“Zero hour.” The Merriam-Webster.com Dictionary, Merriam-Webster Inc., https://www.merriam-webster.com/dictionary/zero%20hour. Accessed 18 January 2020.

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More Definitions for zero hour

zero hour

noun

English Language Learners Definition of zero hour

: the time at which an event (such as a military attack) is scheduled to begin

More from Merriam-Webster on zero hour

Thesaurus: All synonyms and antonyms for zero hour

Rhyming Dictionary: Words that rhyme with zero hour

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