The most common and most likely answer to this crossword clue is the 5 letter word ATOLL
I've seen this crossword clue in The Times
A
T
O
L
L
More clues leading to the result ATOLL
- Bikini, say, shows most of top everyone’s admitted
- Charge to land on a tropical paradise?
- Island everyone goes round first, not last
- Set of twelve letters, last of them for island
- Single fee for the main feature
- A ring or chain in water
- String of islands having a charge for crossing?
- Bikini is article to put on last in local pool
- A charge for a bunch of keys?
- M’s predecessors left bomb test site
Buddy explains!

The straight part
We know that "island" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case island = atoll.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ATOLL mean?
ATOLL noun- A type of island consisting of a ribbon reef that nearly or entirely surrounds a lagoon and supports, in most cases, one to many islets on the reef platform. Atolls have a unique geology, so not all islands with a reef and a lagoon are atolls