formal vs black-tie

formal is a noun but black-tie is not a noun.

Word	Noun	Adjective	Verb	Adverb
formal	Yes	Yes	No	No
black-tie	No	Yes	No	No

formal (noun)	black-tie (noun)
a gown for evening wear
a lavish dance requiring formal attire

formal (adjective)	black-tie (adjective)
being in accord with established forms and conventions and requirements (as e.g. of formal dress)	moderately formal; requiring a dinner jacket
(of spoken and written language) adhering to traditional standards of correctness and without casual, contracted, and colloquial forms
refined or imposing in manner or appearance; befitting a royal court
logically deductive
represented in simplified or symbolic form
characteristic of or befitting a person in authority