from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The unnamed day on which an operation or offensive is to be launched.
- n. The day on which the Allied forces invaded France during World War II (June 6, 1944).
from the GNU version of the Collaborative International Dictionary of English
- n. 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.
- n. 6 June 1944, the day of the landing in France, by troops allied against the Germans in World War II.
- n. the day for commencement or execution of any elaborate planned activity; -- often used jocosely.
D (abbr. of day) + day.(American Heritage® Dictionary of the English Language, Fourth Edition)