My one wasted cash (5)
I believe the answer is:
money
'cash' is the definition.
(cash is a type of money)
'my one wasted' is the wordplay.
'wasted' indicates an anagram.
'my'+'one'='myone'
'myone' with letters rearranged gives 'MONEY'.
(Other definitions for money that I've seen before include "tin" , "The 6 [NECESSARY]" , "Lucre" , "It's the root of all evil" , "Coins, banknotes, etc" .)