Island that's taken over island that's taken over island (6)
I believe the answer is:
tahiti
'island' is the definition.
(I know that Tahiti is a island)
'taken over island that's taken over island' is the wordplay.
'taken over' shows that the letters should be reversed in order.
'island' becomes 'i' (geographical abbreviation).
'taken over' is an insertion indicator (some letters taken over or around others).
'island' becomes 'i' (geographical abbreviation).
'i' placed inside 'that' is 'tihat'.
'tihat' in reverse letter order is 'tahit'.
'tahit'+'i'='TAHITI'
'that's' acts as a link.
(Other definitions for tahiti that I've seen before include "South Pacific island where both Robert Louis Stevenson and Paul Gauguin spent time" , "Pacific island associated with Gauguin" , "I hit at this exotic island" , "South Pacific island, associated with Robert Louis Stevenson" , "Society member" .)