adjective. So implausible as to elicit disbelief; unbelievable.

adjective. Astonishing, extraordinary, or extreme.

Not credible; that cannot be credited; surpassing the possibility of belief.

Surpassing belief as to what is possible; hard to believe; unimaginable; inconceivable.

adjective. Not credible; surpassing belief; too extraordinary and improbable to admit of belief; unlikely; marvelous; fabulous.

adjective. Amazing; astonishing; awe-inspiring.

adjective. Marvelous; profoundly affecting; wonderful.

adjective. beyond belief or understanding

"Of the obstinate effort to bring about an armed intervention, on the lines marked out by Russell’s letter to Palmerston from Gotha, 17 September, 1862, nothing could be said beyond Gladstone’s plea in excuse for his speech in pursuance of the same effort, that it was “the most singular and palpable error, ” “the least excusable, ” “a mistake of incredible grossness, ” which passed defence; but while Gladstone threw himself on the mercy of the public for his speech, he attempted no excuse for Lord Russell who led him into the “incredible grossness” of announcing the Foreign Secretary’s intent."