Surreptitious action (7)
I believe the answer is:
stealth
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">surreptitious action</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 stealth that I've seen before include "Cautious and surreptitious action or movement" , "Unseen machination" , "By which taxes go up" , "Slyness" , "The last (anag.)" .)