Definition of "vane"

A weather vane.  examples

Any of several usually relatively thin, rigid, flat, or sometimes curved surfaces radially mounted along an axis, as a blade in a turbine or a sail on a windmill, that is turned by or used to turn a fluid.  examples

(ornithology) The flattened, web-like part of a feather, consisting of a series of barbs on either side of the shaft.

(navigation) A sight on a sextant or compass.  examples

(weaponry) One of the metal guidance or stabilizing fins attached to the tail of a bomb or other missile.  examples