D-day
Americannoun
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Military. the day, usually unspecified, set for the beginning of a planned attack.
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June 6, 1944, the day of the invasion of western Europe by Allied forces in World War II.
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Informal. any day of special significance, as one marking an important event or goal.
noun
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the day, June 6, 1944, on which the Allied invasion of Europe began
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the day on which any large-scale operation is planned to start
Etymology
Origin of D-day
First recorded in 1918; D (for day ) + day; the same pattern as H-hour
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.