Cetacean (5)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cetacean</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that whale is a type of cetacean)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for whale that I've seen before include "monster" , "one in the water?" , "Maybe humpback" , "Aquatic mammal" , "Mammoth marine mammal" .)