Definition of: windmill

(wind′mil′) noun
1. A mill consisting of a tower within which is a shaft having at the top a horizontal axis which bears a rudder at one end and at the other a system of adjustable slats, wings, or sails which, in revolving, transmit motion to a pump, millstone, or the like.
2. Anything resembling a windmill.
3. An imaginary wrong, evil, or foe: usually in the phrase, to fight (or tilt at) windmills, in allusion to Don Quixote's combat with windmills, which he mistook for giants.