Part of eye (4)
I believe the answer is:
iris
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">part of eye</span>' is the definition.<br/ ><span class="explanation-format__explanation">('iris' is part of 'eye')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for iris that I've seen before include "Fleur-de-lis" , "Flower - rainbow" , "Woman" , "is 21[WOMAN], perhaps" , "Plant with sword-shaped leaves" .)