Pet hate (7)
I believe the answer is:
bugbear
'pet hate' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for bugbear that I've seen before include "Cause of excessive anxiety" , "Object of obsessive, foolish fear" , "constant worry" , "Nasty goblin - cause of fear" , "Cause of great distress" .)