n. - A contrivance attached to some elevated object for the purpose of showing which way the wind blows; a weathercock. It is usually a plate or strip of metal, or slip of wood, often cut into some fanciful form, and placed upon a perpendicular axis around which it moves freely.
n. - Any flat, extended surface attached to an axis and moved by the wind; as, the vane of a windmill; hence, a similar fixture of any form moved in or by water, air, or other fluid; as, the vane of a screw propeller, a fan blower, an anemometer, etc.
n. - The rhachis and web of a feather taken together.
n. - One of the sights of a compass, quadrant, etc.