black tie vs eveningwear

black tie and eveningwear both are nouns.

Word	Noun	Adjective	Verb	Adverb
black tie	Yes	No	No	No
eveningwear	Yes	No	No	No

As nouns, eveningwear is a hypernym of black tie; that is, eveningwear is a word with a broader meaning than black tie:

Other hypernyms of black tie include evening clothes, evening dress, formalwear.

black tie (noun)	eveningwear (noun)
a black bow tie worn with a dinner jacket	attire to wear on formal occasions in the evening
semiformal evening dress for men