This is not dumbness, or denseness, or illiteracy, but belligerent unenlightenment.
Certainly it frequently leaves them inarticulate almost to dumbness.
"Something'll come of the dumbness," he prophesied to himself.
Cally Heth, indeed, stood in a dumbness which she seemed powerless to break.
Perhaps she herself had been sufficient reason for his dumbness.
dumbness sets the brute below the man: Silence elevates the man above the brute.
Molly says, at length awakening to the fact of her lover's dumbness.
He remembered how he had been shocked to dumbness years before when someone in the neighborhood had died.
She was dumb before him, and her dumbness cut Jane to the heart.
It was the house of darkness, the house of dumbness, the house of suffocation.
Old English dumb "silent, unable to speak," from PIE *dheubh- "confusion, stupefaction, dizziness," from root *dheu- (1) "dust, mist, vapor, smoke," and related notions of "defective perception or wits."
The Old English, Old Saxon (dumb), Gothic (dumbs), and Old Norse (dumbr) forms of the word meant only "mute, speechless;" in Old High German (thumb) it meant both this and "stupid," and in Modern German this latter became the only sense. Meaning "foolish, ignorant" was occasionally in Middle English, but modern use (1823) comes from influence of German dumm. Related: dumber; dumbest.
Applied to silent contrivances, hence dumbwaiter. As a verb, in late Old English, "to become mute;" c.1600, "to make mute." To dumb (something) down is from 1933.