complete or total (used as an intensifier--typically when stressing how bad something is)
If she isn’t she’s utterly bad.
Gilbert Blythe was trying to make Anne Shirley look at him and failing utterly, because Anne was at that moment totally oblivious not only to the very existence of Gilbert Blythe, but of every other scholar in Avonlea school itself.
It was bad enough to be singled out for punishment from among a dozen equally guilty ones; it was worse still to be sent to sit with a boy, but that that boy should be Gilbert Blythe was heaping insult on injury to a degree utterly unbearable.
Oh, Marilla, you little know how utterly wretched I am.
Diana flung the paper on the table and herself on Anne’s bed, utterly breathless and incapable of further speech.
There are no more uses of "utter" identified with this meaning, but check unspecified meaning below.
Show samples from other sources
She suffered utter devastation when her child died in the accident.
Gossamers glimmered like threads of silver among the trees and the fir boughs and tassels seemed to utter friendly speech.
She clasped her hands together, gave a piercing shriek, and then flung herself face downward on the bed, crying and writhing in an utter abandonment of disappointment and despair.
For a moment Marilla looked things not lawful to be uttered.
There’s a white lady walks along the brook just about this time of the night and wrings her hands and utters wailing cries.
"You did just splendidly, Anne," puffed Diana, recovering sufficiently to sit up and speak, for Anne, starry eyed and rapt, had not uttered a word.
Her knees trembled, her heart fluttered, a horrible faintness came over her; not a word could she utter, and the next moment she would have fled from the platform despite the humiliation which, she felt, must ever after be her portion if she did so.