Flat broad limb of aquatic animals (7)
I believe the answer is:
flipper
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">flat broad limb of aquatic animals</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 flipper that I've seen before include "Limb used for swimming" , "Flat broad limb of aquatic animals" , "feature of dolphin?" , "Shoe for swimming" , "Seal/turtle limb" .)