Great Britain vs supergrass

Great Britain and supergrass both are nouns.

Word	Noun	Adjective	Verb	Adverb
Great Britain	Yes	No	No	No
supergrass	Yes	No	No	No

Great Britain (noun)	supergrass (noun)
an island comprising England and Scotland and Wales	a police informer who implicates many people
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