zero-hourhttp://www.oed.com/dictionary/zero-hour_n%3Ftab%3Dmeaning_and_usezero hour, n.
Revised 2014

zero hournoun

  1. 1.
    1915–
    The time at which a military operation is scheduled to begin. Also in extended use: the time at which any (typically significant) event is scheduled to take place.
    1. 1915
      At 5:05 A. M. Sept. 25 a message came to the dugout that the ‘zero’ hour, that is, the time the gas was to be started, would be at 5:50 A. M.
      New York Times 9 November 2/3
    2. 1917
      The coming of the zero hour of 3.30 in the morning.
      W. Beach Thomas, With British on Somme ii. v
    3. 1927
      Zero hour—the six o'clock shift waits to go on.
      New Yorker 22 October 48/2 (caption)
    4. 1939
      Your duties will not begin till after dinner. Zero hour is at nine-thirty sharp.
      P. G. Wodehouse, Uncle Fred in Springtime xviii. 269
    5. 1953
      Incidentally, zero hour for tax-payments is approaching.
      A. Huxley, Letter 2 February (1969) 664
    6. 2007
      Almost all the elements for terror attacks were complete except for setting the zero hour for the attacks.
      Washington Post (Nexis) 28 April a12
  2. 2.
    1930–
    The time at which a person feels at his or her lowest. Cf. zero n. A.2.
    Apparently an isolated use.
    1. 1930
      Psychologists have fixed 11 a.m. as the zero hour of the worker.
      Daily Express 23 May 1/6
  3. 3.
    1939–
    The hour from which a new cycle of time is measured; spec. midnight, as the beginning of the day.
    1. 1939
      Methought..I heard at zero hour as 'twere the peal of vixen's laughter among midnight's chimes.
      J. Joyce, Finnegans Wake iii. 403
    2. 1942
      The interval between zero hour and noon..called A. M. (ante-meridian).
      D. Polowe, Navigation for Mariners & Aviators xii. 152
    3. 1959
      Dickinson habitually passed over the conventional middle of the night as the zero hour, when villages are asleep and unaware of time, preferring midday as the hour when eternity begins.
      ELH vol. 26 416
    4. 2007
      The ten second count-down began and got louder and louder as it approached zero hour. On the stroke of midnight loud cheers erupted.
      C. Beckford-Brady, Sweet Home, Jamaica vol. II. ii. 45

Originally published as part of the entry for zero, n. & adj.

zero hour, n. was revised in June 2014.

zero hour, n. was last modified in July 2023.