Dull-witted (6)
I believe the answer is:
obtuse
'dull-witted' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for obtuse that I've seen before include "boneheaded?" , "Dopey" , "Slow of understanding" , "Lacking in insight" , "A 3dn between 90 and 180 degrees" .)