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• D-day
  D-day

  noun

  the day, usually unspecified, set for the beginning of a planned attack.
• D-Day
  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.

D-day

American  

[dee-dey] / ˈdiˌdeɪ /

Or D-Day

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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D-day British  

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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D-Day Cultural  

1. 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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Etymology

Origin of D-day

First recorded in 1918; D (for day ) + day; the same pattern as H-hour

Example Sentences

If you’re skeptical about how exciting a movie about the weather on D-day might be, “Pressure” takes that as a creative challenge, an argumentative stance from which to start.

From Los Angeles Times • May 29, 2026

“He wrote two letters on the eve of D-day: what happens in success and what happens in failure,” Maras says.

From Los Angeles Times • May 29, 2026

Eisenhower, in particular, felt the magnitude of D-day.

From Los Angeles Times • May 29, 2026

“In the D-day sequence at the end, there are various real-life shots of the soldiers landing on the beaches,” Maras says.

From Los Angeles Times • May 29, 2026

Danny Akee always seemed to have a funny story to tell, even about D-day on Saipan.

From "Code Talker: A Novel About the Navajo Marines of World War Two" by Joseph Bruchac