Move furtively; telltale (5)
I believe the answer is:
sneak
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">move furtively</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">telltale</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for sneak that I've seen before include "thief" , "Creep" , "Underhanded tell-tale" , "To go stealthily" , "Steal" .)