Noun

1. The cardinal number that is the sum of four and one
2. One of a pair of decorations projecting above the rear fenders of an automobile
3. One of a set of parallel slats in a door or window to admit air and reject rain
4. A shoe for swimming; the paddle-like front is an aid in swimming (especially underwater)
5. A stabilizer on a ship that resembles the fin of a fish
6. Organ of locomotion and balance in fishes and some other aquatic animals

Verb

1. Equip (a car) with fins
2. Propel oneself through the water in a finning motion
3. Show the fins above the water while swimming