The Collaborative International Dictionary of English v.0.48:

Aurora \Au*ro"ra\, n.; pl. E. Auroras, L. (rarely used)
   Auror[ae]. [L. aurora, for ausosa, akin to Gr. ?, ?, dawn,
   Skr. ushas, and E. east.]
   1. The rising light of the morning; the dawn of day; the
      redness of the sky just before the sun rises.
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   2. The rise, dawn, or beginning. --Hawthorne.
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   3. (Class. Myth.) The Roman personification of the dawn of
      day; the goddess of the morning. The poets represented her
      a rising out of the ocean, in a chariot, with rosy fingers
      dropping gentle dew.
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   4. (Bot.) A species of crowfoot. --Johnson.
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   5. The aurora borealis or aurora australis (northern or
      southern lights).
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   Aurora borealis, i. e., northern daybreak; popularly called
      northern lights. A luminous meteoric phenomenon, visible
      only at night, and supposed to be of electrical origin.
      This species of light usually appears in streams,
      ascending toward the zenith from a dusky line or bank, a
      few degrees above the northern horizon; when reaching
      south beyond the zenith, it forms what is called the
      corona, about a spot in the heavens toward which the
      dipping needle points. Occasionally the aurora appears as
      an arch of light across the heavens from east to west.
      Sometimes it assumes a wavy appearance, and the streams of
      light are then called merry dancers. They assume a variety
      of colors, from a pale red or yellow to a deep red or
      blood color. The

   Aurora australisis a corresponding phenomenon in the
      southern hemisphere, the streams of light ascending in the
      same manner from near the southern horizon.
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WordNet (r) 3.0 (2006):

aurora borealis
    n 1: the aurora of the northern hemisphere [syn: aurora
         borealis, northern lights]