to make someone a dunce or to treat them as if they were stupid; to call or declare someone foolish.
From be- (causative prefix) + dunce (from John Duns Scotus, a medieval philosopher whose name became synonymous with a dull student). The verb means to make or treat as a dunce.
The word 'dunce' comes from a real person's name—John Duns Scotus—and because students disliked his philosophy, his name became an insult! That's how specific historical moments can completely change a word's meaning.
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