Britain vs GB

Britain and GB both are nouns.

Word	Noun	Adjective	Verb	Adverb
Britain	Yes	No	No	No
GB	Yes	No	No	No

Britain (noun)	GB (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	an island comprising England and Scotland and Wales
	a unit of information equal to 1024 mebibytes or 2^30 (1,073,741,824) bytes
	a unit of information equal to 1000 megabytes or 10^9 (1,000,000,000) bytes
	a highly toxic chemical nerve agent that inhibits the activity of cholinesterase