Puzzling, mysterious (9)
I believe the answer is:
enigmatic
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">puzzling</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</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 "Difficult to interpret" , "Puzzling, like the Sphinx" , "Like a puzzle" , "Mystifying" , "with a mystery ingredient" .)