Energy, speed (3)
I believe the answer is:
zip
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">energy</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that energy can be written as zip)</span><br/ ><br/ >'<span class="explanation-format__original">speed</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that speed can be written as zip)</span><br/ ><br/ ></span>
(Other definitions for zip that I've seen before include "closer" , "Nothing < close up" , "Locking device with two toothed edges and a sliding tab" , "drive" , "Type of fastener" .)