Tell-tale (5)
I believe the answer is:
sneak
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">tell-tale</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 sneak that I've seen before include "peach" , "Snitcher" , "Underhanded tell-tale" , "Creep" , "To go stealthily" .)