Bugbear, bête noire (4)
I believe the answer is:
bane
I believe this is a double definition.
'bugbear' is the first definition.
(I've seen this in another clue)
'bete noire' is the second definition.
(I've seen this in another clue)
(Other definitions for bane that I've seen before include "Affliction, cause of distress" , "Source of misery" , "it causes misery" , "Something causing misery or distress" , "Cause of great distress, rhymes with rule" .)