ineffable, unnameable, unspeakable, unutterable - too sacred to be uttered
Example:- the ineffable name of the Deity
abominable, atrocious, awful, dreadful, painful, terrible, unspeakable - exceptionally bad or displeasing
Example:- atrocious taste
indefinable, indescribable, ineffable, unspeakable, untellable, unutterable - defying expression or description
Example:- indefinable yearnings