Flightless marine bird (7)
I believe the answer is:
penguin
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">flightless marine 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 penguin that I've seen before include "King or emperor?" , "Waddling bird" , "Black-and-white antarctic bird" , "Swimming bird" , "King's an example" .)