Security Service vs Great Britain

Security Service and Great Britain both are nouns.

Word	Noun	Adjective	Verb	Adverb
Security Service	Yes	No	No	No
Great Britain	Yes	No	No	No

Security Service (noun)	Great Britain (noun)
the government agency in the United Kingdom that is responsible for internal security and counterintelligence on British territory	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