Definition of "Fin" :

noun: organ of locomotion and balance in fishes and some other aquatic animals

noun: a stabilizer on a ship that resembles the fin of a fish

noun: a shoe for swimming; the paddle-like front is an aid in swimming (especially underwater)

noun: one of a set of parallel slats in a door or window to admit air and reject rain

noun: one of a pair of decorations projecting above the rear fenders of an automobile

noun: the cardinal number that is the sum of four and one

verb: show the fins above the water while swimming

"The sharks were finning near the surface."

verb: propel oneself through the water in a finning motion

verb: equip (a car) with fins