World's rarest goose (4)
I believe the answer is:
nene
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">world's rarest goose</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 nene that I've seen before include "Flower" , "Northants river" , "Northampton's river" , "River navigable to Northampton" , "River of Peterborough; goose" .)