Doc's housemate is a peevish little fellow (6)
I believe the answer is:
grumpy
'fellow' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for grumpy that I've seen before include "Bad-tempered and out of sorts, like one of the Seven Dwarfs" , "Surly, ill-tempered" , "Churlish" , "Black-faced" , "Peevish" .)