vane

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A weathervane.
• noun 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 moved by or used to move a fluid.
• noun The flattened, weblike part of a feather, consisting of a series of barbs on either side of the shaft.
• noun The movable target on a leveling rod.
• noun A sight on a quadrant or compass.
• noun One of the metal guidance or stabilizing fins attached to the tail of a bomb or other missile.

from The Century Dictionary.

• noun A flag or pennon.—
• noun A weathercock; a device which is moved by the wind in such a manner as to show the wind's direction; a weathervane.
• noun A device used on shipboard to answer the purpose of a weathercock: generally called dogvane.
• noun A device similar to a weather-vane, attached to an axis, and having a surface exposed to a moving current, as in an anemometer or a water-meter.
• noun In ornithology, the web of a feather on either side of the shaft; the pogonium; the vexillum. Also used of an arrow. See feather, and cuts under aftershaft and penciling.
• noun One of the plates or blades of a windmill, a screw propeller, and the like. See cuts under screw propeller (under screw), and smoke-jack.
• noun In surveying-instruments: A horizontal piece of wood or metal slipping on a levelingstaff.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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.
• noun Any flat, extended surface attached to an axis and moved by the wind; ; hence, a similar fixture of any form moved in or by water, air, or other fluid.
• noun (Zoöl.) The rhachis and web of a feather taken together.
• noun One of the sights of a compass, quadrant, etc.
• noun (Surv.) Same as Target, 3.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun countable A weather vane.
• noun 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.
• noun ornithology The flattened, web-like part of a feather, consisting of a series of barbs on either side of the shaft.
• noun A sight on a sextant or compass.
• noun One of the metal guidance or stabilizing fins attached to the tail of a bomb or other missile.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun flat surface that rotates and pushes against air or water
• noun the flattened weblike part of a feather consisting of a series of barbs on either side of the shaft
• noun mechanical device attached to an elevated structure; rotates freely to show the direction of the wind
• noun a fin attached to the tail of an arrow, bomb or missile in order to stabilize or guide it