Britain vs peer of the realm

Britain and peer of the realm both are nouns.

Word	Noun	Adjective	Verb	Adverb
Britain	Yes	No	No	No
peer of the realm	Yes	No	No	No

Britain (noun)	peer of the realm (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	a peer who is entitled to sit in the House of Lords