either of a pair of fins situated just behind the head in fishes that help control the direction of movement | organ of locomotion and balance in fishes and some other aquatic animals |
| a stabilizer on a ship that resembles the fin of a fish |
| one of a set of parallel slats in a door or window to admit air and reject rain |
| a shoe for swimming; the paddle-like front is an aid in swimming (especially underwater) |
| one of a pair of decorations projecting above the rear fenders of an automobile |
| the cardinal number that is the sum of four and one |