air brake

noun

1. a brake or system of brakes operated by compressed air.
2. Aeronautics. a device for reducing the air speed of an aircraft by increasing its drag.
3. a device for stopping the sails of a windmill by disrupting the flow of air around them.

noun

1. a brake operated by compressed air, esp in heavy vehicles and trains
2. Also called: dive brake an articulated flap or small parachute for reducing the speed of an aircraft
3. a rotary fan or propeller connected to a shaft to reduce its speed