ro·tor / ˈrōtər/ • n. a rotary part of a machine or vehicle, in particular: ∎ a hub with a number of radiating airfoils that is rotated in an approximately horizontal plane to provide the lift for a rotary-wing aircraft. ∎ the rotating assembly in a turbine, esp. a wind turbine. ∎ the armature of an electric motor. ∎ the rotating part of the distributor of an internal combustion engine that successively makes and breaks electrical contacts so that each spark plug fires in turn. ∎ the rotating container in a centrifuge. ∎ the rotary winder of a clockwork watch. ∎ Meteorol. a large eddy in which the air circulates around a horizontal axis, esp. in the lee of a mountain.