Oomph; fastener (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">oomph</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">fastener</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that zip is a type of fastener)</span><br/ ><br/ ></span>
(Other definitions for zip that I've seen before include "drive" , "Locking device with two toothed edges and a sliding tab" , "Energy or clothes fastener" , "Fastening device" , "required in open-and-shut case?" .)