ineffable
1. [ adjective ] defying expression or description
Synonyms: unspeakable indescribable untellable unutterable indefinable
Examples:

"indefinable yearnings" "indescribable beauty" "ineffable ecstasy" "inexpressible anguish" "unspeakable happiness" "unutterable contempt" "a thing of untellable splendor"

Related terms: inexpressible
2. [ adjective ] too sacred to be uttered
Synonyms: unspeakable unutterable unnameable
Examples:

"the ineffable name of the Deity"

Related terms: sacred
Similar spelling:   ineffably