Limiting fanatic, separatists uprising adapt (6)
I believe the answer is:
attune
'adapt' is the definition.
(I've seen this in another clue)
'limiting fanatic separatists uprising' is the wordplay.
'limiting' means one lot of letters goes inside another.
'fanatic' becomes 'nut' (I've seen this in another clue).
'separatists' becomes 'eta' (ETA, Basque separatist group).
'uprising' says the letters should be written backwards.
'nut' put into 'eta' is 'enutta'.
'enutta' back-to-front is 'ATTUNE'.
(Other definitions for attune that I've seen before include "Harmonise as with musical instrument" , "Get used to" , "Acclimatise" , "Harmonise or adapt, say mind to idea" , "Orient" .)