Intelligible only to the initiated (8)
I believe the answer is:
esoteric
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">intelligible only to the initiated</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 esoteric that I've seen before include "Abstruse; secret" , "Secret, private" , "Privileged or confidential among coteries" , "Mysterious to all but a chosen few" , "Aimed at a few" .)