Source : Webster's Revised Unabridged Dictionary (1913)

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

         Sighed and looked unutterable things.    --Thomson.
   -- {Un*ut"ter*a*ble*ness}, n. -- {Un*ut"ter*a*bly}, adv.