Esoteric, recondite (6)
I believe the answer is:
arcane
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">esoteric</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >'<span class="explanation-format__original">recondite</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for arcane that I've seen before include "Requiring secret or mysterious knowledge" , "Mysterious, secret or obscure" , "Ace ran, being mysterious" , "Esoteric, mysterious" , "Mysterious like a crane" .)