Private parts at last held by naughty coterie (8)
I believe the answer is:
esoteric
'private' is the definition.
(associated in meaning)
'parts at last held by naughty coterie' is the wordplay.
'at last' suggests the final letters.
'held by' indicates putting letters inside.
'naughty' indicates anagramming the letters.
The last letter of 'parts' is 's'.
'coterie' with letters rearranged gives 'eoteric'.
's' going within 'eoteric' is 'ESOTERIC'.
(Other definitions for esoteric that I've seen before include "unintelligible to outsiders" , "known to a few" , "Aimed at a few" , "exclusive" , "of rarefied tastes" .)