Remembrance Day vs Remembrance Sunday

Remembrance Day and Remembrance Sunday both are nouns.

Word	Noun	Adjective	Verb	Adverb
Remembrance Day	Yes	No	No	No
Remembrance Sunday	Yes	No	No	No

As nouns, Remembrance Day and Remembrance Sunday are synonyms defined as:

Remembrance Day and Remembrance Sunday: the Sunday nearest to November 11 when those who died in World War I and World War II are commemorated

Other synonyms of Remembrance Day include Poppy Day.

Remembrance Day (noun)	Remembrance Sunday (noun)
the Sunday nearest to November 11 when those who died in World War I and World War II are commemorated	the Sunday nearest to November 11 when those who died in World War I and World War II are commemorated