Dolphin (7)
I believe the answer is:
grampus
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">dolphin</span>' is the definition.<br/ ><span class="explanation-format__explanation">(grampus is a kind of dolphin)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for grampus that I've seen before include "Killler-whale" , "Killer-whale" , "Marine mammal (heavy breather)" , "Popular name for a killer whale" , "Dolphin - killer whale" .)