the.com/vane

means A thin, pivoting blade mounted high up that turns with the wind to show which direction it's blowing from.

from From Old English 'fana,' meaning flag or banner — the cloth pennant that early weather-readers watched flapping atop poles before anyone thought to make one out of metal. 'Fana' is related to the Latin-rooted word that gives us 'banner' and 'banneret,' and distantly to 'vexillum,' a Roman military standard — all words for cloth signaling intent or direction before vanes made it literal.