Source : Webster's Revised Unabridged Dictionary (1913)

Indescribable \In`de*scrib"a*ble\, a.
   Incapable of being described. -- {In`de*scrib"a*bly}, adv.

Source : WordNet®

indescribable
     adj : defying expression or description; "indefinable yearnings";
           "indescribable beauty"; "ineffable ecstasy";
           "inexpressible anguish"; "unspeakable happiness";
           "unutterable contempt"; "a thing of untellable
           splendor" [syn: {indefinable}, {ineffable}, {unspeakable},
            {untellable}, {unutterable}]