We found 29 dictionaries that define the word d-day:

General (22 matching dictionaries)

1. D-Day, D-day: Merriam-Webster
2. D-Day: Oxford Learner's Dictionaries
3. D-day: American Heritage Dictionary of the English Language
4. D-day, D-day: Collins English Dictionary
5. D-day: Vocabulary.com
6. D-Day, D-day, d-day: Wordnik
7. D-Day, d-day: Cambridge Advanced Learner's Dictionary
8. D-Day: Wiktionary
9. D-day: Webster's New World College Dictionary, 4th Ed.
10. D-day: The Wordsmyth English Dictionary-Thesaurus
11. D-day: Infoplease Dictionary
12. D-Day: Dictionary.com
13. D-day: Online Etymology Dictionary
14. D-Day, D-day: Wikipedia, the Free Encyclopedia
15. D-day: Rhymezone
16. D-Day: Stammtisch Beau Fleuve Acronyms
17. d-day: FreeDictionary.org
18. d-day: Mnemonic Dictionary
19. D-day: TheFreeDictionary.com
20. D-Day: Merriam-Webster

Art (1 matching dictionary)

21. Glossary of Stamp Collecting Terms (No longer online)

Computing (1 matching dictionary)

22. D-day: Encyclopedia

Miscellaneous (2 matching dictionaries)

23. D-DAY: Acronym Finder
24. AbbreviationZ (No longer online)

Slang (1 matching dictionary)

25. The D-day: Urban Dictionary

Tech (2 matching dictionaries)

26. DOD Dictionary of Military Terms: Joint Acronyms and Abbreviations (No longer online)
27. DOD Dictionary of Military Terms (No longer online)

(Note: See d-days as well.)

Definitions from WordNet (D-day) ▸ noun:  day of the allied landing in France, World War II Similar: 6 june 1944, X-Day, Y-Day, Jedburgh, invasion stripes, Freedom Day, A-Day, V-Day, Dominion Day, Dexit, more... Types: D-Day of, more... Phrases: D-Day Daily Telegraph crossword security alarm, National D-Day Memorial, D-Day Dodgers, D-Day naval deceptions, D-Day the Sixth of June, more... ▸ Word origin ▸ Words similar to d-day ▸ Usage examples for d-day ▸ Idioms related to d-day ▸ Wikipedia articles (New!) ▸ Popular adjectives describing d-day ▸ Words that often appear near d-day ▸ Rhymes of d-day ▸ Invented words related to d-day