Nothing; put an end to (3)
I believe the answer is:
nix
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">nothing</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(nix can mean nothing)</span><br/ ><br/ >'<span class="explanation-format__original">put an end to</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for nix that I've seen before include "Nothing (sl.)" , "Spiteful water spirit" , "0" , "Cancel" , "Watch out for" .)