/ Dictionary / Index D D-day: Meaning and Definition of Find definitions for: D-day Pronunciation: (dē'dā"), [key] — n. 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. any day of special significance, as one marking an important event or goal. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: d-day (Thesaurus) DD DDP Related Content Daily Word Quiz: eureka Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language