arterial road vs Great Britain

arterial road and Great Britain both are nouns.

Word	Noun	Adjective	Verb	Adverb
arterial road	Yes	No	No	No
Great Britain	Yes	No	No	No

arterial road (noun)	Great Britain (noun)
a major or main route	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