windsock

/ˈwɪndsɑːk/
noun
  1. A long, cone-shaped cloth tube open at both ends, mounted on a pole to show the direction and strength of the wind, typically at airports or airfields.
    • A windsock flapping straight out means strong winds.
    • The pilot checked the windsock before landing to see which way the wind was blowing.
    • The small airport had a windsock next to the runway.