U.K. vs in

U.K. and in both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.K.	Yes	No	No	No
in	Yes	Yes	No	Yes

U.K. (noun)	in (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 unit of length equal to one twelfth of a foot

U.K. (adverb)	in (adverb)
	to or toward the inside of