vane

(noun) mechanical device attached to an elevated structure; rotates freely to show the direction of the wind. Synonyms: weathervane, weather vane, wind vane.

(noun) a fin attached to the tail of an arrow, bomb or missile in order to stabilize or guide it.

(noun) flat surface that rotates and pushes against air or water. Synonyms: blade.

(noun) the flattened weblike part of a feather consisting of a series of barbs on either side of the shaft. Synonyms: web.