unthinkable

Impossible to imagine; inconceivable.

Not worth considering because of being socially unacceptable, too difficult, or too risky.

Abhorrent; monstrous.

That cannot be made an object of thought; that cannot be thought; incogitable.

Incapable of being believed; incredible.

Inconceivable or unimaginable; extremely improbable in a way that goes against common sense.

incapable of being conceived or considered