UK vs buttoned-up

UK is a noun but buttoned-up is not a noun.

Word	Noun	Adjective	Verb	Adverb
UK	Yes	No	No	No
buttoned-up	No	Yes	No	No

UK (noun)	buttoned-up (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

UK (adjective)	buttoned-up (adjective)
	conservative in professional manner
	(British colloquial) not inclined to conversation