Unit of electric potential (4)
I believe the answer is:
volt
'unit of electric potential' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for volt that I've seen before include "Electrical SI unit named after a pioneering Italian physicist, d. 1827" , "Unit of electric force" , "A measure of electricity" , "Electricity unit" , "Electrical unit of measurement" .)