Security Service vs Britain

Security Service and Britain both are nouns.

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

Security Service (noun)	Britain (noun)
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