Shark's stabilizer (3)
I believe the answer is:
fin
'shark's stabilizer' 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 "Part of an aircraft's tail" , "Fishy appendage" , "Swimmer's flipper" , "Found on a fish" , "Aerodynamic surface" .)