noun1. 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
2. the set of vanes or sails that drives such a mill
3. Also called: whirligig British 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
US and Canadian name: pinwheel 4. an imaginary opponent or evil (esp in the phrase tilt at or fight windmills)
5. a small air-driven propeller fitted to a light aircraft to drive auxiliary equipment
Compare ram-air turbine 6. an informal name for helicopter
7. an informal name for propeller (sense 1)
8. an informal name for accommodation bill
verb9. to move or cause to move like the arms of a windmill
10. (intransitive) (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