Noun

1. A machine which translates linear motion of wind to rotational motion by means of adjustable vanes called sails.
2. The structure containing such machinery.
3. A child's toy consisting of vanes mounted on a stick that rotate when blown by a person or by the wind.
4. A dunk where the dunker swings his arm in a circular motion before throwing the ball through the hoop.
5. A guitar move where the strumming hand mimics a turning windmill.

Verb

1. To rotate with a sweeping motion.

   She ran down the hill, windmilling her arms with glee.

2. Of a rotating part of a machine, to become disengaged and rotate freely.

   The axle broke and the wheel windmilled in place briefly before careening through the wall.