Water bird; frogman (5)
I believe the answer is:
diver
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">water bird</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">frogman</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that frogman can be written as diver)</span><br/ ><br/ ></span>
(Other definitions for diver that I've seen before include "One plunges head first into water" , "Frogman" , "Large waterbird" , "Water bird" , "Drive (anag.)" .)