unspeakable

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.

Impossible to speak about.

It is true that during the first week hardly a day passed that Erskine did not address himself to Watt, on the subject of Watt's duties. But in the first week Watt's words had not yet begun to fail him, or Watt's world to become unspeakable.

Unfit or not permitted to be spoken or described.

The miser will remember his hoard of gold, the robber his ill-gotten wealth, the angry and revengeful and merciless murderers their deeds of blood and violence in which they revelled, the impure and adulterous the unspeakable and filthy pleasures in which they delighted.

Extremely bad or objectionable.

an unspeakable fool

an unspeakable play

That cannot be referenced in source code, due to having no usable name.

an instance of an unspeakable type

unspeakable field names

Something that cannot or must not be spoken about.

Near-synonym: unthinkable

The longer we don't speak about the unspeakables, the more harm they do to the relationship.