unmentionable

un- +‎ mentionable

unmentionable (comparative more unmentionable, superlative most unmentionable)

1. Too embarrassing or shocking to be discussed.

   Antonym: mentionable

• unmentionables
• unmentionably

unmentionable (plural unmentionables)

1. Something not to be discussed in polite society.
   • 1983 December 10, Mary F. Miller, “Personal advertisement”, in Gay Community News, volume 11, number 21, page 19:

     I'm a lesbian female, 20 years old and my most outstanding features are my pierced unmentionable and my eyes.

   • 1995, Virginia Schroeder Burnham, William H. Hampton, Since Time Began, page 43:

     He was taught from childhood that the world does not condone homosexuality and that it is an unmentionable of decent people.

   • 2014, Andrew Hodges, Alan Turing: The Enigma, page 100:

     Here, after all, was the circle round which Forster passed the manuscript of his novel Maurice which conveyed so much about being 'an unmentionable of the Oscar Wilde sort'.

• “unmentionable”, in Cambridge English Dictionary, Cambridge, Cambridgeshire: Cambridge University Press, 1999–present.
• “unmentionable”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.
• “unmentionable” in Longman Dictionary of Contemporary English, Longman.