Difficult, possessing nothing, to save (5)
I believe the answer is:
hoard
'to save' is the definition.
(hoard can mean to save or keep)
'difficult possessing nothing' is the wordplay.
'difficult' becomes 'hard' (synonyms).
'possessing' indicates putting letters inside.
'nothing' becomes 'O' (O resembles 0).
'hard' going around 'o' is 'HOARD'.
(Other definitions for hoard that I've seen before include "Secret stash" , "Stash of treasure" , "Valuable store" , "A lot of people" , "Store, usually hidden" .)