D-day vs 6 June 1944

D-day and 6 June 1944 both are nouns.

Word	Noun	Adjective	Verb	Adverb
D-day	Yes	No	No	No
6 June 1944	Yes	No	No	No

As nouns, D-day and 6 June 1944 are synonyms defined as:

D-day and 6 June 1944: date of the Allied landing in France, World War II

Other synonyms of D-day include Normandy landings.

D-day (noun)	6 June 1944 (noun)
date of the Allied landing in France, World War II	date of the Allied landing in France, World War II