obtuse - ub-TYOUS - dull, slow, pea-brained, vapid, vacuous
Example: "The story featured a pair of contrasting personalities; one was sharp & quick-witted, the other obtuse to the extreme."
As a starter: and as a former teacher in English, I hope to add to reader's vocabulary by presenting a word a day in simple terms that anyone can understand - from current use in publications, radio,TV, etc. Remember: use a new word three times in a day and it's yours forever!