windmill (Noun) — A mill that is powered by the wind.
windmill (Noun) — Generator that extracts usable energy from winds.
windmill (Noun) — A toy consisting of vanes of coloured paper or plastic that is pinned to a stick and spins when it is pointed into the wind.
windmill (Verb) — Rotate one's arms with a sweeping motion. ex. "she ran down the hill, windmilling her arms with glee"
windmill (Verb) — (of a rotating part of a machine) become disengaged and rotate freely. ex. "The axle broke and the wheel windmilled in place"