D-day

n.	1.	(Mil.) the day designated for the beginning of a planned attack by a military force; in communications the day is often otherwise unspecified for security reasons; as, the day before D-day the troops will move into position.
	2.	6 June 1944, the day of the landing in France, by troops allied against the Germans in World War II.
	3.	the day for commencement or execution of any elaborate planned activity; - often used jocosely.

Noun

1.

D-day - day of the allied landing in France, World War II Synonyms: 6 June 1944

6 June 1944, date, day of the month