a building with equipment for grinding grain into flour that is driven by the power of the wind turning long arms (called sails) 风车磨房 
a tall, thin structure with parts that turn round, used to change the power of the wind into electricity （通过转动将风能转化为电能的）风车 - (British English) (North American English pinwheel)
a toy with curved plastic parts that form the shape of a flower that turns round on the end of a stick when you blow on it 玩具风车
Idioms
tilt at windmills
to waste your energy attacking imaginary enemies 攻击假想敌；庸人自扰