Spoil rotten (6)
I believe the answer is:
pamper
'spoil rotten' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pamper that I've seen before include "Treat indulgently" , "Mollycoddle" , "Treat with over-indulgence" , "Spoil, cosset" , "Overindulge (someone)" .)