noun Etymology: from its being marked by the count of zero in a countdown Date: 1917 1. the hour at which a planned military operation is scheduled to start, the time at which a usually significant or notable event is scheduled to take place, a time when a vital decision or decisive change must be made
ZERO HOUR
Meaning of ZERO HOUR in English
Merriam Webster. Explanatory English dictionary Merriam Webster. Толковый словарь английского языка Мерриам-Уэбстер. 2012