Source : Webster's Revised Unabridged Dictionary (1913)

Mirror \Mir"ror\, n. [OE. mirour, F. miroir, OF. also mireor,
   fr. (assumed) LL. miratorium, fr. mirare to look at, L.
   mirari to wonder. See {Marvel}, and cf. {Miracle},
   {Mirador}.]
   1. A looking-glass or a speculum; any glass or polished
      substance that forms images by the reflection of rays of
      light.

            And in her hand she held a mirror bright, Wherein
            her face she often view[`e]d fair.    --Spenser.

   2. That which gives a true representation, or in which a true
      image may be seen; hence, a pattern; an exemplar.

            She is mirour of all courtesy.        --Chaucer.

            O goddess, heavenly bright, Mirror of grace and
            majesty divine.                       --Spenser.

   3. (Zo["o]l.) See {Speculum}.

   {Mirror carp} (Zo["o]l.), a domesticated variety of the carp,
      having only three or fur rows of very large scales side.
      

   {Mirror plate}.
      (a) A flat glass mirror without a frame.
      (b) Flat glass used for making mirrors.

   {Mirror writing}, a manner or form of backward writing,
      making manuscript resembling in slant and order of letters
      the reflection of ordinary writing in a mirror. The
      substitution of this manner of writing for the common
      manner is a symptom of some kinds of nervous disease.

Mirror \Mir"ror\, v. t. [imp. & p. p. {Mirrored}; p. pr. & vb.
   n. {Mirroring}.]
   To reflect, as in a mirror.

Source : WordNet®

mirror
     n 1: polished surface that forms images by reflecting light
     2: a faithful depiction or reflection; "the best mirror is an
        old friend"

mirror
     v 1: reflect as if in a mirror; "The smallest pond at night
          mirrors the firmament above"
     2: reflect or resemble; "The plane crash in Milan mirrored the
        attack in the World Trade Center"

Source : Free On-Line Dictionary of Computing

mirror
     
        1.  Writing duplicate data to more than one
        device (usually two {hard disks}), in order to protect against
        loss of data in the event of device failure.  This technique
        may be implemented in either hardware (sharing a {disk
        controller} and cables) or in software.  It is a common
        feature of {RAID} systems.
     
        Several {operating systems} support software disk mirroring or
        {disk-duplexing}, e.g. {Novell NetWare}.
     
        See also {Redundant Array of Independent Disks}.
     
        Interestingly, when this technique is used with {magnetic
        tape} storage systems, it is usually called "twinning".
     
        A less expensive alternative, which only limits the amount of
        data loss, is to make regular {backup}s from a single disk to
        {magnetic tape}.
     
        2.  An {archive site} or {web site} which keeps a
        copy of some or all files at another site so as to make them
        more quickly available to local users and to reduce the load
        on the source site.  Such mirroring is usually done for
        specific whole directories or files on a specific remote
        server as opposed to a {cache} or {proxy server} which keeps
        copies of everything that is requested via it.
     
        For example, src.doc.ic.ac.uk is the main UK mirror for the
        {GNU} archive at gnu.org.  There are also several
        {mirrors of this dictionary
        (http://www.foldoc.org/foldoc/mirrors.html)}.
     
        (1998-06-11)