- any of various machines for grinding, pumping, etc., driven by the force of the wind acting upon a number of vanes or sails.
- (loosely) a wind generator; wind plant.
- a small air turbine with blades, like those of an airplane propeller, exposed on a moving aircraft and driven by the air, used to operate gasoline pumps, radio apparatus, etc.
- an imaginary opponent, wrong, etc. (in allusion to Cervantes' Don Quixote): to tilt at windmills.
- (of a propeller engine or turbojet engine) to rotate or cause to rotate solely under the force of a passing airstream.
- a machine for grinding or pumping driven by a set of adjustable vanes or sails that are caused to turn by the force of the wind
- the set of vanes or sails that drives such a mill
- a toy consisting of plastic or paper vanes attached to a stick in such a manner that they revolve like the sails of a windmill
- an imaginary opponent or evil (esp in the phrase tilt at or fight windmills)
- a small air-driven propeller fitted to a light aircraft to drive auxiliary equipment
- an informal name for helicopter
- an informal name for propeller (def. 1)
- to move or cause to move like the arms of a windmill
- an informal name for accommodation bill
- (of an aircraft propeller, rotor of a turbine, etc) to rotate as a result of the force of a current of air rather than under power
