Battered troopers capturing island back (9)
I believe the answer is:
posterior
'back' is the definition.
(similar in meaning)
'battered troopers capturing island' is the wordplay.
'battered' indicates an anagram.
'capturing' is an insertion indicator.
'island' becomes 'i' (geographical abbreviation).
'troopers' anagrammed gives 'posteror'.
'posteror' placed around 'i' is 'POSTERIOR'.
(Other definitions for posterior that I've seen before include "Further back; bottom" , "Rear" , "later" , "Behind" , "Hindquarters" .)