brassiere vs unmentionable

brassiere and unmentionable both are nouns.

Word	Noun	Adjective	Verb	Adverb
brassiere	Yes	No	No	No
unmentionable	Yes	Yes	No	No

As nouns, unmentionable is a hypernym of brassiere; that is, unmentionable is a word with a broader meaning than brassiere:

Other hypernyms of brassiere include undergarment, woman's clothing.

brassiere (noun)	unmentionable (noun)
an undergarment worn by women to support their breasts	a garment worn under other garments

brassiere (adjective)	unmentionable (adjective)
	unsuitable or forbidden as a topic of conversation