Furtive, sly (6)
I believe the answer is:
sneaky
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">furtive</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that furtive can be written as sneaky)</span><br/ ><br/ >'<span class="explanation-format__original">sly</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for sneaky that I've seen before include "Cunning" , "Sly and devious" , "Furtive or given to telling tales" , "Being furtive or underhanded" , "Deceitful, underhand" .)