Completely motionless (5-5)
I believe the answer is:
stock-still
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">completely motionless</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for stock-still that I've seen before include "Completely motionless" , "Without any movement" , "Absolutely motionless" .)