in vs Great Britain

in and Great Britain both are nouns.

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

in (noun)	Great Britain (noun)
a unit of length equal to one twelfth of a foot	an island comprising England and Scotland and Wales
	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

in (adverb)	Great Britain (adverb)
to or toward the inside of