Sullen and ill-tempered (6)
I believe the answer is:
morose
'sullen and ill-tempered' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for morose that I've seen before include "Rarely" , "Sullen. bad-tempered" , "Sullen and ill-tempered" , "in a grumpy mood" , "Silent, gloomy and ill-tempered" .)