Definition of zero hour in English:

zero hour

Line breaks: zero hour

noun

The time at which a planned operation, typically a military one, is set to begin.
More example sentences
  • Accompanied by your other three team members, you begin at zero hour of the Clone Wars.
  • A few minor adjustments were made to the presentation plan, and we set 3 o'clock as zero hour.
  • As zero hour approached, Spanish-language radio stations broadcast appeals for all able-bodied Cuban-Americans to help.
Synonyms
the appointed time, the appointed hour, the crucial moment, the vital moment, the critical moment, the moment of truth, the point/moment of decision, the Rubicon, the critical point, the crux
informal the crunch

Origin

First World War: from zero + hour.

Definition of zero hour in:

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Pronunciation: ˈbɪmb(ə)l
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walk or travel at a leisurely pace