ineffable in WordNet English dictionary

1. defying expression or description
   "indefinable yearnings"; "indescribable beauty"; "ineffable ecstasy"; "inexpressible anguish"; "unspeakable happiness"; "unutterable contempt"; "a thing of untellable splendor"
   indefinable  indescribable  ineffable  unspeakable  untellable  unutterable 
   
2. too sacred to be uttered
   "the ineffable name of the Deity"
   ineffable  unnameable  unspeakable  unutterable