unmentionable thing

How to use unmentionable thing in a sentence

• He drew Jurgis out, and heard all about his life all but the one unmentionable thing; and then he told stories about his own life.

  The Jungle | Upton Sinclair

• As is common in most modern discussions the unmentionable thing is the pivot of the whole discussion.

  What's Wrong With The World | G.K. Chesterton