Iodine reaction (5)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">iodine reaction</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for sting that I've seen before include "English musician, b. 1951 -- a sudden pain" , "The pain caused by bee or nettle" , "Entrapment operation; sharp pain" , "18, sharp pain" , "Bee/wasp wound" .)