Incapable of being spoken or uttered / Impossible to speak about. / Unfit or not permitted to be spoken or described. / Extremely bad or objectionable.

The condition or quality of being unspeakable.

present participle of unspeak

Silent, not talking. / Mute, unable to speak for physical or psychological reasons.

Third-person singular simple present indicative form of unspeak

In an unspeakable manner.

(rare) To retract what one has spoken, to unsay.

unspeakableness