Evacuate middle of next island (7)
I believe the answer is:
excrete
'evacuate' is the definition.
'middle of next island' is the wordplay.
'middle of' means to look at the middle letters.
'island' becomes 'crete' (Greek island).
The middle of 'next' is 'ex'.
'ex'+'crete'='EXCRETE'
(Other definitions for excrete that I've seen before include "Eliminate (from the body)" , "Expel (waste) from the body" , "Defecate" .)