Fin

One of the appendages of a fish, used to propel itself and to manoeuvre/maneuver.

"The fish's fins minimize water flow."

A similar appendage of a cetacean or other marine animal.

"a dolphin's fin"

A thin, rigid component of an aircraft, extending from the fuselage and used to stabilise and steer the aircraft.

"The fin stabilises the plane in flight."

A similar structure on the tail of a bomb, used to help keep it on course.

To cut the fins from a fish, shark, etc.

(Of a fish) to swim with the dorsal fin above the surface of the water.

To swim in the manner of a fish.

"A neutrally buoyant diver does not need to fin to maintain depth."

To provide (a motor vehicle etc) with fins.