Constant nuisance (4)
I believe the answer is:
bane
'constant nuisance' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bane that I've seen before include "Affliction, cause of distress" , "Something causing misery or distress" , "Blight" , "scourge" , "it causes misery" .)