unspeakable in WordNet English dictionary

1. 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"
   atrocious  abominable  awful  dreadful  painful  terrible  unspeakable 
   
2. 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 
   
3. too sacred to be uttered
   "the ineffable name of the Deity"
   ineffable  unnameable  unspeakable  unutterable