vane
/veɪn; ven/ n
1 arrow or pointer on the top of a building, turned by the wind so as to show its direction 风向标; 风信旗.
2 blade of a propeller, sail of a windmill, or a similar device with a flat surface acted on or moved by wind or water （螺旋桨、 风车、 轮机等的）翼, 叶片.