Unutterable

Un‐ut″ter‐a‐ble (?), a. Not utterable; incapable of being spoken or voiced; inexpressible; ineffable; unspeakable; as, unutterable anguish.

Sighed and looked unutterable things. Thomson.

— Un‐ut″ter‐a‐ble‐ness, n. — Un‐ut″ter‐a‐bly, adv.