What is the meaning of fin?

noun

• The cardinal number that is the sum of four and one.
  • synonyms: five, 5, V, cinque, quint, quintet, fivesome, quintuplet, pentad, Phoebe, Little Phoebe
• One of a pair of decorations projecting above the rear fenders of an automobile.
  • synonyms: tail fin, tailfin
• One of a set of parallel slats in a door or window to admit air and reject rain.
  • synonyms: louver, louvre
• A shoe for swimming; the paddle-like front is an aid in swimming (especially underwater.
  • synonyms: flipper
• A stabilizer on a ship that resembles the fin of a fish.
• Organ of locomotion and balance in fishes and some other aquatic animals.

verb

• Equip (a car) with fins.
• Propel oneself through the water in a finning motion.
• Show the fins above the water while swimming.
  • usage: "The sharks were finning near the surface"
  • synonyms: break water