Flipper (3)
I believe the answer is:
fin
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">flipper</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for fin that I've seen before include "Fish propeller; end (Fr.)" , "Aerodynamic surface" , "Swimmer" , "Thin projection for fish to steer itself" , "A fish uses it to steer itself" .)