Lagoon surrounder (5)
I believe the answer is:
atoll
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lagoon surrounder</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for atoll that I've seen before include "Pacific coral island" , "Allot (anag.)" , "Ring-shaped coral island" , "Circular coral reef" , "Coral circle" .)