rotor

noun

1. any of various rotating mechanical parts; specif.,
   1. the rotating part of a motor, dynamo, etc.
   2. in the distributor of a gasoline engine, the part that momentarily connects each spark plug wire to the high voltage from the coil
   3. in disc brakes, the part to which the wheel is usually mounted
2. a system of airfoils, together with their hub, that rotates around a vertical axis, as on a helicopter

Origin: contr. of rotator