UK vs red-brick

UK is a noun but red-brick is not a noun.

Word	Noun	Adjective	Verb	Adverb
UK	Yes	No	No	No
red-brick	No	Yes	No	No

UK (noun)	red-brick (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)	red-brick (adjective)
	of or relating to British universities founded in the late 19th century or the 20th century