Keep secret; skin (4)
I believe the answer is:
hide
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">keep secret</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">skin</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(hide is a kind of skin)</span><br/ ><br/ ></span>
(Other definitions for hide that I've seen before include "Animal's tough skin" , "Conceal with leather" , "mask" , "Bury" , "Place to observe wildlife" .)