The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         Ye rejoice with joy unspeakable and full of glory. --1
                                                  Pet. i. 8.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unspeakably
    adv 1: to an inexpressible degree; "she was looking very young
           tonight, and, as usual, indescribably beautiful, in a
           simple strapless dress of a green and white silky cotton"
           [syn: ineffably, indescribably, unutterably,
           unspeakably]