noun

1. a flat piece of metal, strip of cloth, etc. set up high to swing with the wind and show which way it is blowing; weather vane
2. any of several flat or curved pieces set around an axle and rotated about it by moving air, water, etc. [the vanes of a windmill], or mechanically rotated to move the air or water [the vanes of a turbine] or to compress the air [the vanes of a supercharger]
3. a projecting fixed or movable plate or strip of metal attached to a rocket, missile, etc. to provide stability or guidance
4. a target set to slide on a leveling rod, for use in surveying
5. any of the sights on a compass, quadrant, etc.
6. 1. the flat part of a feather with barbs; web
   2. a feather on an arrow, used to stabilize flight

Etymology: S Brit var. of fane, small flag or pennon < OE fana, a flag < PGmc *fanan- < IE base *pan- > pane