From Longman Dictionary of Contemporary Englishunmentionableun‧men‧tion‧a‧ble /ʌnˈmenʃənəbəl/ adjective RUDE/IMPOLITERUDE/OBSCENEtoo shocking or embarrassing to talk about unmentionable scandals
Examples from the Corpus
unmentionable• This behaviour was unmentionable a few years before, although it probably did take place.• Stalin had long been unmentionable and Volkogonov was said to be using closed secret archives.• She hoped she hadn't caught an unmentionable disease from her visit to the news-theatre.• Let us begin with a few simple, crucial, and apparently unmentionable facts about a typical high-school classroom.• Divorce, desertion, and illegitimacy were considered almost unmentionable scandals.• Miguelito yelled up that the man should do something unmentionable to himself. 