Supplies punishment once (6)
I believe the answer is:
stocks
This clue is a double definition.
'supplies' is the first definition.
(stocking is a kind of supplying)
'punishment once' is the second definition.
(as in putting someone in the stocks)
(Other definitions for stocks that I've seen before include "In which miscreant is locked" , "Amounts of goods kept by traders" , "Plants; form of punishment" , "Frame for shipbuilding - form of punishment" , "Keeps" .)