Fin

The definition for Fin in Wikipedia:

A fin is a surface used to produce lift and thrust or to steer while traveling in water, air, or other fluid media. The first use of the word was for the limbs of fish, but has been extended to include other animal limbs and man-made devices.
The foremost use of fins is to ensure the directional stability of an object moving through a fluid such as water or air and may be seen in the use of fletching on arrows and fins at the rear of some missiles, rockets, self-propelled torpedoes, and kinetic energy penetrators. They are typically "planar" (shaped like small wings), although grid fins are sometimes used in specialized cases.
Moving fins may be used to propel an object through lateral thrust (see mechanics).

To editorialize: Fin is used to produce lift and thrust, to steer while traveling through air. Fin has been extended to include other animals (my fin). The foremost use of Fin is to ensure the directional stability moving through air.