Perplexing; mysterious (9)
I believe the answer is:
enigmatic
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">perplexing</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">mysterious</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for enigmatic that I've seen before include "Obscure, puzzling" , "Ambiguous or puzzling" , "Puzzling, like the Sphinx" , "Like a puzzle" , "Mysterious or puzzling, like Mona Lisa's smile" .)