Source : Webster's Revised Unabridged Dictionary (1913)

Viewer \View"er\, n.
   1. One who views or examines.

   2. (Law) A person appointed to inspect highways, fences, or
      the like, and to report upon the same.

   3. The superintendent of a coal mine. [Eng.]

Source : WordNet®

viewer
     n 1: a close observer; someone who looks at something (such as an
          exhibition of some kind); "the spectators applauded the
          performance"; "television viewers"; "sky watchers
          discovered a new star" [syn: {spectator}, {witness}, {watcher},
           {looker}]
     2: an optical device for viewing photographic transparencies

Source : Free On-Line Dictionary of Computing

viewer
     
         A program to allow a file to be read (or played) but
        not changed.  Viewers are often freely distributable, even
        when the editor application is not.  This allows you to create
        files with the editor and make the viewer available to other
        users to view your files, e.g. on a {web site}.  Examples
        include the Word and Adobe Acrobat viewers.
     
        (1997-08-29)