The Collaborative International Dictionary of English v.0.48:

Unutterable \Un*ut"ter*a*ble\, a.
   Not utterable; incapable of being spoken or voiced;
   inexpressible; ineffable; unspeakable; as, unutterable
   anguish.
   [1913 Webster]

         Sighed and looked unutterable things.    --Thomson.
   [1913 Webster] -- Un*ut"ter*a*ble*ness, n. --
   Un*ut"ter*a*bly, adv.
   [1913 Webster]