Diving waterbird (5)
I believe the answer is:
grebe
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">diving waterbird</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 grebe that I've seen before include "Diving bird which may be crested" , "Diver" , "Aquatic bird that builds floating nests" , "Swimmer" , "Flier" .)