The Collaborative International Dictionary of English v.0.48:

Rune \Rune\ (r[udd]n), n. [AS. r[=u]n a rune, a secret, a
   mystery; akin to Icel. r[=u]n, OHG. & Goth. r[=u]na a secret,
   secret colloquy, G. & Dan. rune rune, and probably to Gr.
   'ereyna^n to search for. Cf. Roun to whisper.]
   1. A letter, or character, belonging to the written language
      of the ancient Norsemen, or Scandinavians; in a wider
      sense, applied to the letters of the ancient nations of
      Northern Europe in general.
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   Note: The Norsemen had a peculiar alphabet, consisting of
         sixteen letters, or characters, called runes, the
         origin of which is lost in the remotest antiquity. The
         signification of the word rune (mystery) seems to
         allude to the fact that originally only a few were
         acquainted with the use of these marks, and that they
         were mostly applied to secret tricks, witchcrafts and
         enchantments. But the runes were also used in
         communication by writing.
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   2. pl. Old Norse poetry expressed in runes.
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            Runes were upon his tongue,
            As on the warrior's sword.            --Longfellow.
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   Rune stone, a stone bearing a runic inscription.
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