Home Counties vs Great Britain

Home Counties and Great Britain both are nouns.

Word	Noun	Adjective	Verb	Adverb
Home Counties	Yes	No	No	No
Great Britain	Yes	No	No	No

Home Counties (noun)	Great Britain (noun)
the English counties surrounding London into which Greater London has expanded	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