Slow-witted (7)
(Another definition for doltish that I've seen is " Dull, stupid".)
'slow-witted' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dense that I've seen before include "Closely-spaced" , "Thick and tightly-packed" , "Thick as undergrowth may be" , "Close-knit" , "Close knit" .)