What is a wethervane?

Answer 1

A weather vane or wind vane is a device which swivels around a central point to indicate the direct of the prevailing wind.

Answer 2

A weather vane is a device that is typically mounted on rooftops to indicate the direction of the wind. It consists of a flat or arrow-shaped plate that rotates freely and points in the direction from which the wind is blowing. Weather vanes are often used as decorative elements on buildings, especially on barns and homes.