black tie vs bow tie

black tie and bow tie both are nouns.

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

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

Other hypernyms of black tie include bow-tie, bowtie.

black tie (noun)	bow tie (noun)
a black bow tie worn with a dinner jacket	a man's tie that ties in a bow
semiformal evening dress for men