Secret coteries broken up (8)
I believe the answer is:
esoteric
'secret' is the definition.
(similar in meaning)
'coteries broken up' is the wordplay.
'broken up' indicates anagramming the letters.
'coteries' is an anagram of 'ESOTERIC'.
(Other definitions for esoteric that I've seen before include "'Abstruse, arcane (8)'" , "unintelligible to outsiders" , "Hard to understand" , "Private, confined to a select group" , "Intelligible only with special knowledge" .)