windmill

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A machine that runs on the energy generated by a wheel of adjustable blades or slats rotated by the wind.
• noun Something, such as a toy pinwheel, that is similar to a windmill in appearance or operation.
• intransitive & transitive verb To move or cause to move like the wheel of a windmill; rotate sweepingly.
• idiom (tilt at windmills) To confront and engage in conflict with an imagined opponent or threat.

from The Century Dictionary.

• noun A mill or machine for grinding, pumping, or other purposes, moved by the wind; a wind-motor; any form of motor for utilizing the pressure of the wind as a motive power.
• noun A visionary scheme; a vain project; a fancy; a chimera.

from the GNU version of the Collaborative International Dictionary of English.

• noun A mill operated by the power of the wind, usually by the action of the wind upon oblique vanes or sails which radiate from a horizontal shaft.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A machine which translates linear motion of wind to rotational motion by means of adjustable vanes called sails.
• noun The structure containing such machinery.
• noun A child's toy consisting of vanes mounted on a stick that rotate when blown by a person or by the wind.
• noun basketball A dunk where the dunker swings his arm in a circular motion before throwing the ball through the hoop.
• noun A guitar move where the strumming hand mimics a turning windmill.
• noun juggling The false shower.
• verb transitive, intransitive To rotate (itself) with a sweeping motion.
• verb intransitive Of a rotating part of a machine, to (become disengaged and) rotate freely.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun generator that extracts usable energy from winds
• noun a mill that is powered by the wind