Great Britain vs Security Service

Great Britain and Security Service both are nouns.

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

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