unmentionable

[1]	undergarment
[2]	unmentionables , underclothes , underclothing , underwear , undergarments , lingerie , (Archaic) small-clothes , (Colloq) underthings , undies , (Brit) smalls , (US) skivvies

adj.

[1]	unspeakable , unutterable , ineffable , taboo , scandalous , forbidden , interdicted , inexpressible
[2]	disgraceful , indecent , immodest , shameful , shocking , appalling , dishonourable , indescribable , obscene , filthy