Great Britain vs police constable

Great Britain and police constable both are nouns.

Word	Noun	Adjective	Verb	Adverb
Great Britain	Yes	No	No	No
police constable	Yes	No	No	No

Great Britain (noun)	police constable (noun)
an island comprising England and Scotland and Wales	a police officer of the lowest rank
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