Literary or old-fashioned term for mental dullness or slowness; not common in everyday speech.
He had a dull-witted expression, and I couldn't tell what he was thinking.
The old man feigned dullness to avoid unnecessary questions.
Compound of 痴 (ち, 'foolish, stupid') and 鈍 (どん, 'dull, slow'). The exact historical derivation is uncertain, but the combination directly conveys mental dullness.