The Collaborative International Dictionary of English v.0.48:

Beacon \Bea"con\ (b[=e]"k'n), n. [OE. bekene, AS. be['a]cen,
   b[=e]cen; akin to OS. b[=o]kan, Fries. baken, beken, sign,
   signal, D. baak, OHG. bouhhan, G. bake; of unknown origin.
   Cf. Beckon.]
   1. A signal fire to notify of the approach of an enemy, or to
      give any notice, commonly of warning.
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            No flaming beacons cast their blaze afar. --Gay.
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   2. A signal, such as that from a lighthouse, or a conspicuous
      mark erected on an eminence near the shore, or moored in
      shoal water, as a guide to mariners.
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   3. A high hill near the shore. [Prov. Eng.]
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   4. That which gives notice of danger.
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            Modest doubt is called
            The beacon of the wise.               --Shak.
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   5. (Navigation) a radio transmitter which emits a
      characteristic signal indication its location, so that
      vehicles may determine their exact location by locating
      the beacon with a radio compass; -- also called radio
      beacon.
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   5. [fig.] that which provides guidance or inspiration; the
      Constitution has been a beacon for civil rights activists.
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   Beacon fire, a signal fire.
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WordNet (r) 3.0 (2006):

beacon fire
    n 1: a fire (usually on a hill or tower) that can be seen from a
         distance [syn: beacon, beacon fire]