A tax for an island (5)
I believe the answer is:
atoll
'island' is the definition.
(I've seen this in another clue)
'a tax for an' is the wordplay.
'a tax' becomes 'toll' (I've seen this in another clue).
'for' says to put letters next to each other (I've seen this in other clues).
'an' becomes 'a'.
'toll' put after 'a' is 'ATOLL'.
(Other definitions for atoll that I've seen before include "Coral circle" , "Coral island surrounding a lagoon" , "tropical paradise?" , "Coral island(s) surrounding a lagoon" , "Coral isle" .)