1.Definition: defying expression or description

"Unspeakable happiness"

Related Adjective(s):indefinable, indescribable, ineffable, untellable, unutterable

2.Definition: exceptionally bad or displeasing

"An unspeakable odor came sweeping into the room"

Related Adjective(s):abominable, atrocious, awful, dreadful, painful, terrible

3.Definition: too sacred to be uttered

Related Adjective(s):ineffable, unnameable, unutterable