Ponder about island’s improper treatment (6)
I believe the answer is:
misuse
'improper treatment' is the definition.
(wrong or improper use)
'ponder about island's' is the wordplay.
'ponder' becomes 'muse' (synonyms).
'about' means one lot of letters goes inside another.
'island's' becomes 'i's' (geographical abbreviation).
'muse' going around 'is' is 'MISUSE'.
(Other definitions for misuse that I've seen before include "Wrongful employment" , "poor employment" , "Improper application" , "bad practice" , "Ill-treatment" .)