Great Britain vs crossbench

Great Britain and crossbench both are nouns.

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

Great Britain (noun)	crossbench (noun)
an island comprising England and Scotland and Wales	any of the seats in the House of Commons used by members who do not vote regularly with either the government or the Opposition
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