White heron (5)
I believe the answer is:
egret
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">white heron</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for egret that I've seen before include "Water-bird, has plume" , "Wader with white plumage" , "Greet (anag) -- wading bird" , "White wading bird" , "one with plume" .)