Esoteric leader of pagans involved in organising choir (6)
I believe the answer is:
orphic
'esoteric' is the definition.
(I've seen this before)
'leader of pagans involved in organising choir' is the wordplay.
'leader of' indicates taking the first letters.
'involved in' means one lot of letters goes inside another.
'organising' indicates anagramming the letters.
The initial letter of 'pagans' is 'p'.
'choir' is an anagram of 'orhic'.
'p' placed inside 'orhic' is 'ORPHIC'.
(Other definitions for orphic that I've seen before include "Relating to Orpheus" , "according to a great musician" , "Of a mythical Greek poet and lyre-player" , "Relating to legendary Greek lyre player" , "Esoteric" .)