Great Britain vs backbench

Great Britain and backbench both are nouns.

Word	Noun	Adjective	Verb	Adverb
Great Britain	Yes	No	No	No
backbench	Yes	No	No	No

Great Britain (noun)	backbench (noun)
an island comprising England and Scotland and Wales	any of the seats occupied by backbenchers in the House of Commons
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