Toothed fastener (3)
I believe the answer is:
zip
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">toothed fastener</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for zip that I've seen before include "drive" , "required in open-and-shut case?" , "Energy (informal); a US code" , "Energy or clothes fastener" , "Sound of bullet passing" .)