Definition of rotor in US English:



  • 1A hub with a number of radiating airfoils that is rotated in an approximately horizontal plane to provide the lift for a helicopter or other rotary-wing aircraft.

    • ‘I could hear the thwapping of helicopter rotors, the grinding of tank treads, the sound of RPG's and bazookas.’
    • ‘The helicopter rises up over the ridge line, the noise of the rotors scattering the targets below.’
    • ‘He raised his suntanned right arm to his face and shielded his eyes from the swirling clouds of dirt and dust kicked up by the Dauphin's rotors.’
    • ‘The helicopters' rotors started turning, first slowly, then faster and faster, making a loud chopping noise as they cut the air.’
    • ‘He opened the door and leapt out while the rotors were still spinning and brushed off his clothes.’
    • ‘The shot was from a news helicopter and Cecil could hear the thudding of the helicopter rotors in the background as the reporter began to speak.’
    • ‘They heard the engine revving and the quickening beat of the rotors.’
    • ‘He walked up to Blaine just as the helicopter rotors disengaged.’
    • ‘The aircraft featured two large rotors located in nacelles on the ends of its wings linked to an air-cooled Daimler Benz 600 engine in the fuselage.’
    • ‘The sound of the helicopter's rumbling rotors became louder, as it flew by directly overhead us, and began hovering over the red smoke.’
    • ‘You'll hear your rotor speeding up and slowing down, and the roar of missiles as they fly by you.’
    • ‘Then the sound of rotors is heard, and they look up, only to see the two Serpent helicopters hovering above them.’
    • ‘Will gave a light two fingered salute to those staying, as the rotors whirred and the chopper left.’
    • ‘He fired up the engine and the rotors began to whirl.’
    • ‘With a soft hum of power the large rotors started up and the officers were off, soaring up to investigate the powerless upper levels of the massive city.’
    • ‘As the rotors slowed, a side hatch opened and the Security Chief climbed out, followed by Director Bakan and their respective aides.’
    • ‘He barely dodged a humongous hammer that flew past him and destroyed the main rotor on one of the remaining helicopters.’
    • ‘The rotors started to spin up and they hurriedly jumped to the roof a few feet below, ducking to avoid the backwash from the spinning propellers as the copter lifted off the heliport and headed into the night skyline.’
    • ‘They were pretty useless when confronted with the high-pitched whine of the rotor's gears directly above our heads.’
    • ‘The aircraft would have launched standing upright like a rocket, but instead of using a blast of fire to take off the pilot would have simply adjusted the thrust and pitch of the rotors as with a helicopter.’
  • 2The rotating assembly in a turbine, especially a wind turbine.

    • ‘Take away the 2.2 birds killed by the rotors, and the balance for wind energy, + 1707.8 birds per turbine a year, is not bad.’
    • ‘Standing at the base of one of the towers, there's only a gentle whoosh as the rotors sweep around.’
    • ‘A fearless reaper, it pivots on its tower to face the wind, propellerlike rotor already scything around, faster and faster.’
    • ‘‘The bigger the rotor, the more wind you can collect,’ Sagrillo explained.’
    • ‘The rotor turns an attached generator, creating electricity with a simple elegance, carving energy from the sky.’
    • ‘She had to return to Southampton and have the turbine rotors completely redesigned and rebuilt.’
    • ‘Should they malfunction or prove insufficient to slow the rotor in high winds, a large disk brake mounted on the generator shaft can smoothly bring the turbine to a halt.’
    • ‘The wind generated by the rotors while sitting on the ground is tremendous.’
    • ‘Wind plant rotors have either two or three blades.’
    • ‘To achieve this same increase using a larger rotor is usually a more expensive choice than placing a smaller rotor on a higher tower where it will receive stronger winds.’
    • ‘The higher-wattage plants, with their large-diameter, low-rotation-per-minute rotors, are designed to capture energy from low wind speeds.’
    1. 2.1 The armature of an electric motor.
    2. 2.2 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.
      • ‘Unlike a piston engine, where reciprocating parts move up and down, the twin rotors in the Mazda just spin around.’
      • ‘Motorists who failed to immobilise their cars, by taking away the rotor arm from the distributor, were liable to find their tyres deflated by the police.’
      • ‘This time we had lost the rotor arm as well and Phil had to sprint back 100 yards to find it.’
      • ‘The heavy impact damaged the rotor arm and though he carried on, Andrew was handicapped by a misfiring engine and could only struggle home sixth.’
      • ‘After 20 minutes he decided the problem was with the rotor arm, and fashioned some wire underneath it to solve the problem.’
      • ‘It might have been tougher for Godfrey had the Cooper S of his competitors not lost nearly 10 minutes right at the start of the Radnor stage with a broken rotor arm.’
      • ‘For example, if D hires a car to P and then removes the rotor arm from it rendering it inoperable, he may be guilty of criminal damage.’
      • ‘While Freestone had a good run on his first experience of the stage, they had a nightmare when a broken rotor arm cost them over two minutes.’
      • ‘Rear rotors are vented on the GT and solid on the V - 6.’
      • ‘I immediately changed the oil, plugs, distributor cap, rotor arm, and a friendly independent specialist fixed the exhaust.’
    3. 2.3 The rotating container in a centrifuge.
      • ‘One junior intelligence analyst thought that although they weren't at all like modern American centrifuge rotors, they might be usable in what are known as a Zippe centrifuge.’
      • ‘The Department of Energy rejected the claim that the country was importing aluminum tubes to produce centrifuge rotors for enriching uranium.’
    4. 2.4 The rotary winder of a clockwork watch.
  • 3Meteorology
    A large eddy in which the air circulates around a horizontal axis, especially in the lee of a mountain.


Early 20th century: formed irregularly from rotator.