Ruin, downfall (7)
I believe the answer is:
undoing
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">ruin</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">downfall</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(both can mean a loss of power or position)</span><br/ ><br/ ></span>
(Other definitions for undoing that I've seen before include "Cause of ruin" , "Taking apart" , "(A person's) ruin or downfall" , "Ruin - disaster" .)