Shark part (3)
I believe the answer is:
fin
'shark part' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for fin that I've seen before include "For movement and balance in fish" , "Aerodynamic surface" , "A fish uses it to steer itself" , "Swimmer's flipper" , "Found on a fish" .)