The Collaborative International Dictionary of English v.0.48:

icon \i"con\ ([imac]"k[o^]n), n. [Also spelled ikon.] [L., fr.
   Gr. e'ikw`n.]
   1. An image or representation; a portrait or pretended
      portrait.
      [1913 Webster]

            Netherlands whose names and icons are published.
                                                  --Hakewill.
      [1913 Webster]

   2. (Gr. Ch.) A sacred picture representing the Virgin Mary,
      Christ, a saint, or a martyr, and having the same function
      as an image of such a person in the Latin Church. The term
      is used especially for a highly stylized and
      conventionalized representation of a holy person, rich in
      symbolism and used in devotional services in many of the
      eastern Orthodox churches, especially the Greek and
      Russian Orthodox Churches.
      [Webster 1913 Suppl. +PJC]

   3. a symbol, especially a symbol whose form suggests its
      meaning or the object it represents.
      [PJC]

   4. (Computers) a graphical symbol for a data object whose
      form suggests the nature or function of the object;
      especially, such a symbol as viewed on the computer
      screen.

   Note: In a graphical user interface, pointing to and clicking
         on an icon may cause any of several types of actions,
         such as opening a file or executing a program,
         depending on how the icon properties are defined.
         [PJC]

   5. any object of uncritical devotion.
      [PJC]

            The former congresswoman and Vice-Presidential
            candidate Geraldine Ferraro is still an icon to many
            party members.                        --The New York
                                                  Times, April
                                                  16, 1998
      [PJC]

   6. an outstanding example of something which has come to
      represent the class of things to which it belongs; a
      paragon; used of persons as well as objects.
      [PJC]

WordNet (r) 3.0 (2006):

ikon
    n 1: a visual representation (of an object or scene or person or
         abstraction) produced on a surface; "they showed us the
         pictures of their wedding"; "a movie is a series of images
         projected so rapidly that the eye integrates them" [syn:
         picture, image, icon, ikon]
    2: a conventional religious painting in oil on a small wooden
       panel; venerated in the Eastern Church [syn: icon, ikon]