Power unit (4)
I believe the answer is:
watt
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">power unit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(unit of power)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for watt that I've seen before include "Unit of power - Scottish inventor" , "Unit of electric power" , "man of power?" , "Scot. engineer; unit of power" , "SI unit of power" .)