Harmful nuisance I supplied money to for a while (9)
I believe the answer is:
pestilent
'harmful' is the definition.
('pestilent' can be similar in meaning to 'harmful')
'nuisance i supplied money to for a while' is the wordplay.
'nuisance' becomes 'pest' (I've seen this before).
'supplied money to for a while' becomes 'lent'.
'pest'+'i'+'lent'='PESTILENT'
(Other definitions for pestilent that I've seen before include "Pernicious" , "Vexatious" , "Plaguey" , "Peel tints (anag) - extremely tiresome" , "Annoying" .)