Boxing Day vs Great Britain

Boxing Day and Great Britain both are nouns.

Word	Noun	Adjective	Verb	Adverb
Boxing Day	Yes	No	No	No
Great Britain	Yes	No	No	No

Boxing Day (noun)	Great Britain (noun)
first weekday after Christmas	an island comprising England and Scotland and Wales
	a monarchy in northwestern Europe occupying most of the British Isles; divided into England and Scotland and Wales and Northern Ireland; `Great Britain' is often used loosely to refer to the United Kingdom