The Collaborative International Dictionary of English v.0.48:

Guidon \Gui"don\, n. [F. guidon, It. guidone. See Guide, v.
   t.]
   1. A small flag or streamer, as that carried by cavalry,
      which is broad at one end and nearly pointed at the other,
      or that used to direct the movements of a body of
      infantry, or to make signals at sea; also, the flag of a
      guild or fraternity. In the United States service, each
      company of cavalry has a guidon.
      [1913 Webster]

            The pendants and guidons were carried by the officer
            of the army.                          --Evelyn.
      [1913 Webster]

   2. One who carries a flag. --Johnson.
      [1913 Webster]

   3. One of a community established at Rome, by Charlemagne, to
      guide pilgrims to the Holy Land.
      [1913 Webster]