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

In Act Two, tensions continue to rise and reach their frightful climax at zero hour detonation. — Paul Ross, Popular Mechanics, "I Am Become Opera: An Atomic Show In the Shadow of Los Alamos," 27 July 2018 His business partner Robert Goldfarb then served as the unpaid trustee for a few years, spending zero hours a week on foundation business, according to tax filings. — Andrea Fuller, WSJ, "Private Charitable Foundations Give Lavish Rewards to Insiders," 29 May 2018

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.