dress up vs attire

dress up is not a noun while attire is a noun.

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

As verbs, dress up and attire are synonyms defined as:

dress up and attire: put on special clothes to appear particularly appealing and attractive

dress up (noun)	attire (noun)
	clothing of a distinctive style or for a particular occasion

dress up (verb)	attire (verb)
put on special clothes to appear particularly appealing and attractive	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