|Noah Webster's Dictionary|
(a.) Incapable of being spoken or voiced; inexpressible; ineffable; unspeakable; as, unutterable anguish.
Unutterable (3 Occurrences)
Romans 8:26 And, in like manner also, the Spirit doth help our weaknesses; for, what we may pray for, as it behoveth 'us', we have not known, but the Spirit himself doth make intercession for us with groanings unutterable, (YLT)
2 Corinthians 12:4 that he was caught away to the paradise, and heard unutterable sayings, that it is not possible for man to speak. (YLT)
1 Peter 1:8 whom not having known you love; in whom, though now you don't see him, yet believing, you rejoice greatly with joy unspeakable and full of glory- (See RSV)