apparel vs dress up

apparel is a noun but dress up is not a noun.

Word	Noun	Adjective	Verb	Adverb
apparel	Yes	No	Yes	No
dress up	No	No	Yes	No

As verbs, dress up is a hyponym of apparel; that is, dress up is a word with a more specific, narrower meaning than apparel:

apparel (noun)	dress up (noun)
clothing in general

apparel (verb)	dress up (verb)
provide with clothes or put clothes on	put on special clothes to appear particularly appealing and attractive
	dress in a costume
	dress in a certain manner
	make something appear superficially attractive
	put a caparison on