police constable vs Great Britain

police constable and Great Britain both are nouns.

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

police constable (noun)	Great Britain (noun)
a police officer of the lowest rank	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