Over-supply (7)
I believe the answer is:
surplus
I believe this clue is a double definition.
'over' is the first definition.
(thesaurus)
'supply' is the second definition.
(thesaurus)
(Other definitions for surplus that I've seen before include "Unneeded extra" , "Excess, overstock" , "Redundant" , "Amount left over" , "Remainder" .)