Potential unit (4)
I believe the answer is:
volt
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">potential unit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(volt is a kind of potential unit)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for volt that I've seen before include "Unit of electric force" , "SI unit of electromotive force" , "Electricity unit" , "A measure of electricity" , "Unit of electric potential difference" .)