Sustained hunger (4)
I believe the answer is:
long
I believe this clue is a double definition.
'sustained' is the first definition.
(I've seen this before)
'hunger' is the second definition.
(both can mean to crave)
(Other definitions for long that I've seen before include "Extensive - pine" , "extended period" , "hunger" , "Thus having been treated by stretcher, perhaps" , "Lengthy - pine" .)