unspeakable

Etymology

From Middle English unspekable, equivalent to un- + speakable.

adj

1. Incapable of being spoken or uttered
   1855-1882, Walt Whitman, Leaves of Grass, book xv, The endless pride and outstretching of man, unspeakable joys and sorrows.
2. Impossible to speak about.
3. Unfit or not permitted to be spoken or described.
4. Extremely bad or objectionable.
   an unspeakable fool
   an unspeakable play
   Yet to my horror I saw in its eaten-away and bone-revealing outlines a leering, abhorrent travesty on the human shape; and in its mouldy, disintegrating apparel an unspeakable quality that chilled me even more. 1926, H.P. Lovecraft, The Outsider
   Anyone who goes into a voting booth on November the 8th and comes out saying, “I feel a hundred percent great about what I just did in there!,” is either lying to themselves, or did something unspeakable in that booth! And that means, as uncomfortable as this is, everyone has to own the floors of whoever you vote for, whether they are a lying handsy narcissistic sociopath, a hawkish Wall Street-friendly embodiment of everything that some people can’t stand about politics, an ill-tempered mountain molester with a radical dangerous tax plan that even he can’t defend, or a conspiracy-pandering political neophyte with no clear understanding of how government operates and who once recorded this folk rap about the virtues of bicycling. Oct 16 2016, “Third Parties”, in Last Week Tonight with John Oliver, season 3, episode 26, John Oliver (actor), via HBO