unspeakable
adj.too terrible or shocking to be described with words. You use this when something is so bad that you cannot even talk about it.
adj.too extreme, intense, or horrific to be expressed in words. Often used to describe profound suffering or moral atrocities.
“The victims suffered unspeakable pain during the war.”
“The documentary reveals the unspeakable conditions inside the abandoned prison during the late nineteenth century.”
“The survivors were left to grapple with the unspeakable trauma of the disaster, finding that language was often insufficient to convey the depth of their loss.”
Typically used attributively before a noun to emphasize the extreme nature of a negative quality.
“Understand the horror: on the day you read this, as on every other, an average of 17 people will die in unspeakable pain, disgust and terror that nothing can relieve.”
From Middle English unspekable, equivalent to un- + speakable.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.