UK vs Security Service

UK and Security Service both are nouns.

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

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