From WordNet (r) 3.0 (2006):
fin
n 1: the cardinal number that is the sum of four and one [syn:
five, 5, V, cinque, quint, quintet, fivesome,
quintuplet, pentad, fin, Phoebe, Little Phoebe]
2: one of a pair of decorations projecting above the rear
fenders of an automobile [syn: tail fin, tailfin, fin]
3: one of a set of parallel slats in a door or window to admit
air and reject rain [syn: louver, louvre, fin]
4: a shoe for swimming; the paddle-like front is an aid in
swimming (especially underwater) [syn: flipper, fin]
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
v 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; "The sharks
were finning near the surface" [syn: fin, break water]