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.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
How to use D-day in a sentence
It must have been one of the big highs of the war, to be in London and hit the pubs during the last two months before D-day.Blood in the Sand: When James Jones Wrote a Grunt’s View of D-Day | James Jones | November 15, 2014 | THE DAILY BEAST
For the citizens of that city, this event has a deeper, more sentimental meaning than even D-day.
Williams interviewed and profiled four D-day veterans, showing his sensitive side without ever seeming maudlin.
D-day was the first successful opposed landing on French territory—the country was held by the Nazis—in over 800 years.D-Day 70th Anniversary Celebrations: Queen, Obama, Merkel, Putin and Cameron in France | Tom Sykes | June 6, 2014 | THE DAILY BEAST
D-day was 70 years ago, and to midshipmen of today, it is all but ancient history.D-Day Historian Craig Symonds Talks About History’s Most Amazing Invasion | Marc Wortman | June 5, 2014 | THE DAILY BEAST
The end of a perfect D-day she tried to grin, her teeth chattering with cold.Dorothy Dixon and the Mystery Plane | Dorothy Wayne
British Dictionary definitions for D-day
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
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Cultural definitions for D-Day
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.