Large aquatic bird (4)
I believe the answer is:
swan
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">large aquatic bird</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for swan that I've seen before include "Large aquatic bird" , "Royal bird" , "Kind of song, in the end" , "Mute, whooper or Bewick's bird" , "The Ugly Duckling's outcome" .)