The Collaborative International Dictionary of English v.0.48:

Vane \Vane\ (v[=a]n), n. [OE. & Prov. E. fane weathercock,
   banner, AS. fana a banner, flag; akin to D. vaan, G. fahne,
   OHG. fano cloth, gund fano flag, Icel. f[=a]ni, Sw. fana,
   Dan. fane, Goth. fana cloth, L. pannus, and perhaps to Gr.
   ph^nos a web, phni`on a bobbin, spool. Cf. Fanon, Pane a
   compartment, panel.]
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   [1913 Webster]
   1. 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.
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            Aye undiscreet, and changing as a vane. --Chaucer.
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   2. 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.
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   3. (Zool.) The rhachis and web of a feather taken together.
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   4. One of the sights of a compass, quadrant, etc.
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   Vane of a leveling staff. (Surv.) Same as Target, 3.
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WordNet (r) 3.0 (2006):

vane
    n 1: mechanical device attached to an elevated structure;
         rotates freely to show the direction of the wind [syn:
         weathervane, weather vane, vane, wind vane]
    2: a fin attached to the tail of an arrow, bomb or missile in
       order to stabilize or guide it
    3: flat surface that rotates and pushes against air or water
       [syn: blade, vane]
    4: the flattened weblike part of a feather consisting of a
       series of barbs on either side of the shaft [syn: vane,
       web]