U.K. vs u

U.K. and u both are nouns.

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

U.K. (noun)	u (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	the 21st letter of the Roman alphabet

U.K. (adjective)	u (adjective)
	(chiefly British) of or appropriate to the upper classes especially in language use