UNUTTERABLY
ineffably, indescribably, unutterably, unspeakably, inexpressibly
(adverb) to an inexpressible degree; “she was looking very young tonight, and, as usual, indescribably beautiful, in a simple strapless dress of a green and white silky cotton”
Source: WordNet® 3.1
Etymology
Adverb
unutterably (comparative more unutterably, superlative most unutterably)
In an unutterable manner.
Source: Wiktionary
UNUTTERABLE
Un*ut"ter*a*ble, a.
Definition: 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.
Source: Webster’s Unabridged Dictionary 1913 Edition