fin

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

The fish's fins minimize water flow.

Then he commenced to talk, really talk. and inside of two flaps of a herring's fin he had me mesmerized, like Eben Holt's boy at the town hall show. He talked about the ills of humanity, and the glories of health and Nature and service and land knows what all.

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 protruding from a projectile, used to help keep it on course.

A similar structure on the bottom of a surfboard, used to help steer it.

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

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

When you spot him finning just under the surface, you move up quietly and present [...] bait, usually a squid.

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.

a five-pound (£5) note; the sum of five pounds.

A five-dollar bill; the sum of five dollars.