A ringing endorsement for the island (5)
I believe the answer is:
atoll
'the island' is the definition.
(I've seen this before)
'a ringing endorsement' is the wordplay.
'ringing endorsement' becomes 'toll' (I can't explain this - if you can you should believe this answer much more).
'a'+'toll'='ATOLL'
'for' is the link.
Can you help me to learn more?
(Other definitions for atoll that I've seen before include "Key" , "land threatened by rising sea levels" , "Ring-shaped coral reef enclosing a lagoon" , "Coral island surrounding a lagoon" , "Coral island(s) surrounding a lagoon" .)