black tie vs bowtie

black tie and bowtie both are nouns.

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

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

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

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