Ctrl-Z command (4)
I believe the answer is:
undo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ctrl-z command</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for undo that I've seen before include "Unfasten or annul" , "Open button or ruin" , "Ruin, destroy" , "Cause to become loose" , "Cause downfall" .)