The Oxford Thesaurus An A-Z Dictionary of Synonyms - unmentionableadj.

1) unspeakable, unutterable, ineffable, taboo, scandalous, forbidden, interdicted; inexpressible: I will not have Karen or her unmentionable boyfriend in this house again! 2 disgraceful, indecent, immodest, shameful, shocking, appalling, dishonourable, indescribable, obscene, filthy: In carnivals, geeks do unmentionable things with live chickens. --n. 3) unmentionables. underclothes, underclothing, underwear, undergarments, lingerie, Archaic small-clothes, Colloq underthings, undies, Brit smalls, US skivvies: The woman next door insists on hanging out her unmentionables in full view of the whole street.