Source : Webster's Revised Unabridged Dictionary (1913)

Unspeakable \Un*speak"a*ble\, a. [Pref. un- not + speakable.]
   Not speakable; incapable of being uttered or adequately
   described; inexpressible; unutterable; ineffable; as,
   unspeakable grief or rage. -- {Un*speak"a*bly}, adv.

         Ye rejoice with joy unspeakable and full of glory. --1
                                                  Pet. i. 8.

Source : WordNet®

unspeakable
     adj 1: defying expression or description; "indefinable yearnings";
            "indescribable beauty"; "ineffable ecstasy";
            "inexpressible anguish"; "unspeakable happiness";
            "unutterable contempt"; "a thing of untellable
            splendor" [syn: {indefinable}, {indescribable}, {ineffable},
             {untellable}, {unutterable}]
     2: exceptionally bad or displeasing; "atrocious taste";
        "abominable workmanship"; "an awful voice"; "dreadful
        manners"; "a painful performance"; "terrible handwriting";
        "an unspeakable odor came sweeping into the room" [syn: {atrocious},
         {abominable}, {awful}, {dreadful}, {painful}, {terrible}]
     3: too sacred to be uttered; "the ineffable name of the Deity"
        [syn: {ineffable}, {unnameable}, {unutterable}]