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D-day

or D-Day

[dee-dey]
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noun
  1. Military. the day, usually unspecified, set for the beginning of a planned attack.
  2. June 6, 1944, the day of the invasion of western Europe by Allied forces in World War II.
  3. Informal. any day of special significance, as one marking an important event or goal.
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Origin of D-day

Dutch (for day) + day; the same pattern as H-hour
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for d-day

D-day

noun
  1. the day, June 6, 1944, on which the Allied invasion of Europe began
  2. the day on which any large-scale operation is planned to start
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Word Origin

C20: from D (ay) -day; compare H-hour
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for d-day

D-day

1918, "date set for the beginning of a military operation," with D as an abbreviation of day, cf. H-hour, also from the same military order of Sept. 7, 1918:

The First Army will attack at H-Hour on D-Day with the object of forcing the evacuation of the St. Mihiel salient. [Field Order No. 8, First Army, A.E.F.]

"They designate the day and hour of the operation when the day and hour have not yet been determined, or where secrecy is essential" [U.S. Army Center of Military History Web site]. Now almost exclusively of June 6, 1944.

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Online Etymology Dictionary, © 2010 Douglas Harper

d-day in Culture

D-Day

The code name for the first day of a military attack, especially the American and British invasion of German-occupied France during World War II on June 6, 1944 (see invasion of Normandy). This marked the beginning of the victory of the Allies in Europe. Germany surrendered less than a year later.

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The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.