Atoll, small island (4)
I believe the answer is:
isle
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">atoll</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">small island</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for isle that I've seen before include "Hawaii, perhaps" , "Such as Man or Bute" , "Eg, eyot or inch" , "I shall hear" , "Christmas or Easter, perhaps" .)