Spooky, sinister (6)
I believe the answer is:
creepy
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">spooky</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">sinister</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for creepy that I've seen before include "Mysterious" , "Spooky" , "Scary, eery" , "Disturbing, crawly" , "Eerie; repellent" .)