Great Britain vs Solway Firth

Great Britain and Solway Firth both are nouns.

Word	Noun	Adjective	Verb	Adverb
Great Britain	Yes	No	No	No
Solway Firth	Yes	No	No	No

Great Britain (noun)	Solway Firth (noun)
an island comprising England and Scotland and Wales	a large firth on the west coast of Britain between England and Scotland
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