Obscure Byzantine coteries (8)
I believe the answer is:
esoteric
'obscure' is the definition.
(I've seen this before)
'byzantine coteries' is the wordplay.
'byzantine' indicates anagramming the letters (byzantine means complex or confusing).
'coteries' anagrammed gives 'ESOTERIC'.
(Other definitions for esoteric that I've seen before include "Intelligible only to informed people in coteries" , "Tie score (anagram)" , "Occult" , "needing privy" , "Privileged or confidential among coteries" .)