Describes hair that's thick and poorly groomed (6)
I believe the answer is:
shaggy
(Other definitions for shaggy that I've seen before include "like the dog in the story" , "Covered with long hair or wool" , "Long and unmanageable (of hair) - Scooby Doo's pal" , "Very hairy, like some dog stories" , "Describes thick and poorly groomed hair" .)