black-tie vs formal

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

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

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

black-tie (adjective)	formal (adjective)
moderately formal; requiring a dinner jacket	being in accord with established forms and conventions and requirements (as e.g. of formal dress)
	(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