Obscure coteries break up
I believe the answer is:
esoteric
'obscure' is the definition.
(requiring specialist knowledge or special interest)
'coteries break up' is the wordplay.
'break up' indicates anagramming the letters.
'coteries' with letters rearranged gives 'ESOTERIC'.
(Other definitions for esoteric that I've seen before include "needing privy" , "unintelligible to outsiders" , "Secret, mysterious" , "hidden" , "I set core up to be mysterious" .)