Discharge, old and bowed (4)
I believe the answer is:
arco
'bowed' is the definition.
(musical term - played with a bow)
'discharge old' is the wordplay.
'discharge' becomes 'arc' (electrical discharge).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'arc'+'o'='ARCO'
'and' is the link.
(Other definitions for arco that I've seen before include "Played with the bow" , "Musical direction" , "bow for players" , "taking a bow" , "which every violinist must grasp" .)