Island's chief accountant (7)
I believe the answer is:
majorca
'island's' is the definition.
(I've seen this before)
'chief accountant' is the wordplay.
'chief' becomes 'major' (I've seen this before).
'accountant' becomes 'ca' (abbreviation for chartered accountant).
'major'+'ca'='MAJORCA'
(Other definitions for majorca that I've seen before include "Largest of the Balearic Islands" , "Main Balearic island" , "Palma its capital" , "Largest Balearic Island" , "Mediterranean island" .)