Undo, unlock (4)
I believe the answer is:
open
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">undo</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(opening is a kind of undoing)</span><br/ ><br/ >'<span class="explanation-format__original">unlock</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 open that I've seen before include "Affording access" , "simple" , "unsealed" , "Overt" , "Not shut up or hidden" .)