<p><strong>Noun</strong></p><ul><li>Any of various machines for grinding, pumping, etc., driven by the force of the wind acting upon a number of vanes or sails.</li><li>(Loosely) a wind generator; wind plant.</li><li><strong>Aeronautics</strong>: 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.</li><li>An imaginary opponent, wrong, etc. (in allusion to Cervantes' <em>Don Quixote</em>): to tilt at windmills.</li></ul><p><strong>Verb</strong></p><ul><li>(Used with or without object) <strong>Aeronautics</strong>: (of a propeller engine or turbojet engine) to rotate or cause to rotate solely under the force of a passing airstream.</li></ul>