- Military. the day, usually unspecified, set for the beginning of a planned attack.
- June 6, 1944, the day of the invasion of western Europe by Allied forces in World War II.
- Informal. any day of special significance, as one marking an important event or goal.
Origin of D-day
Examples from the Web for d-day
Williams interviewed and profiled four D-Day veterans, showing his sensitive side without ever seeming maudlin.Hillary Clinton’s Network Massage
June 10, 2014
D-Day was the first successful opposed landing on French territory—the country was held by the Nazis—in over 800 years.
D-Day was 70 years ago, and to midshipmen of today, it is all but ancient history.
There is a tendency to conceive of the Allied landings on D-Day as a single event, but in fact it was just the first step.
Did Churchill and Roosevelt agree about the when, where, and how of D-Day and the invasion of France?
- the day, June 6, 1944, on which the Allied invasion of Europe began
- the day on which any large-scale operation is planned to start
Word Origin and History for 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.