Webster's Revised Unabridged Dictionary · 1913

Incredible

Incredible , adjective

[Latin incredibilis: compare Old French incredible. See In- not, and Credible.]

Not credible; surpassing belief; too extraordinary and improbable to admit of belief; unlikely; marvelous; fabulous.
Why should it be thought a thing incredible with you, that God should raise the dead? — Acts xxvi. 8