Aeronautics. a system of rotating airfoils, as the horizontal ones of a helicopter or of the compressor of a jet engine.
any of a number of tall, cylindrical devices mounted on a special ship (rotor ship) and rotated in such a way that the Magnus effect of wind impinging on the cylinders is used to drive and maneuver the vessel.
(in a self-winding watch) a weight eccentrically mounted on an arbor for keeping the mainspring wound.
1873, irregular shortening of rotator, originally in mathematics. Mechanical sense is attested from 1903; specifically of helicopters from 1930. Rototiller (with tiller) is a proprietary name in U.S., attested from 1923.