Tract·or n.
 1. That which draws, or is used for drawing.
 2. pl. Med. Two small, pointed rods of metal, formerly used in the treatment called Perkinism.
 5. Aviation A propeller screw placed in front of the supporting planes of an aeroplane instead of behind them, so that it exerts a pull instead of a push; -- called also Tractor screw and Tractor propeller.
 6. Aviation An airplane having one or more tractor propellers; -- called also tractor airplane.

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 Tractor screw or  Tractor propeller. Aviation A propeller screw placed in front of the supporting planes of an airplane instead of behind them, so that it exerts a pull instead of a push. Hence, Tractor monoplane, Tractor biplane, etc.  This is the most common arrangement for propellers on modern airplanes.

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