Command-Z, on a Mac (4)
I believe the answer is:
undo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">command-z on a mac</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for undo that I've seen before include "Cancel -- annul -- reverse" , "Dismantle - destroy" , "Overturn" , "set free" , "Cause to become loose" .)