Answer:

FIN

Answer	Crossword Clue
FIN	60's car appendage
FIN	Shark's appendage
FIN	'59 Caddy adornment

FIN	Fiver
FIN	Feature of 50's autos
FIN	Shark sighting, often
FIN	A shark's scares you in the water
FIN	Half a sawbuck
FIN	Semisawbuck
FIN	'50s car feature
FIN	Torpedo feature

FIN	Hull projection
FIN	Fish's steering mechanism
FIN	Five-spot
FIN	"Jaws" omen
FIN	Bygone auto ornament
FIN	Flipper
FIN	Snorkeling accessory
FIN	Rocket feature

FIN	'50s car embellishment
FIN	Old El Dorado feature
FIN	"Jaws" sighting
FIN	Five-dollar bill, in slang
FIN	Sturgeon steerer
FIN	Shark "trademark"
FIN	Five-dollar bill, slangily
FIN	Bad thing for a surfer to see

FIN	Feature of some late '50s cars
FIN	Dorsal appendage
FIN	Vertical stabilizer
FIN	It may be dorsal
FIN	Five-dollar bill
FIN	Flying fish's "wing"
FIN	Flipper's flipper
FIN	Shark ... soup

FIN	Yacht appendage
FIN	Aquatic appendage
FIN	Ominous sighting in "Jaws"
FIN	Pickerel propeller
FIN	Albacore appendage