Cash drain, possibly (5)
I believe the answer is:
dinar
'cash' is the definition.
(I know that dinar is a currency)
'drain possibly' is the wordplay.
'possibly' indicates an anagram.
'drain' is an anagram of 'DINAR'.
(Other definitions for dinar that I've seen before include "Currency of several Arab countries" , "Iraqi capital" , "Currency unit of Algeria, Libya etc" , "Monetary unit of Algeria" , "money" .)