Что такое fin? Что такое fin? A membranous appendage extending from the body of a fish or other aquatic animal, used for propelling, steering, or balancing the body in the water.Something resembling a fin in shape or function, as:A fixed or movable airfoil used to stabilize an aircraft, missile, or projectile in flight. A thin, usually curved projection attached to the rear bottom of a surfboard for stability.A projecting vane used for cooling, as on a radiator or an engine cylinder.See tail fin.See flipper.To equip with fins.To emerge with the fins above water.To swim, as a fish.To lash the water with the fins. Used of a dying whale.Slang A five-dollar bill.