fin

Noun

• organ of locomotion and balance in fishes and some other aquatic animals

• a stabilizer on a ship that resembles the fin of a fish

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

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

• 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

Verb

• show the fins above the water while swimming
  • The sharks were finning near the surface
    

• propel oneself through the water in a finning motion

• equip (a car) with fins

Related words

• Synonyms: 
  flipper , louver , louvre , tail fin , tailfin , break water