The Collaborative International Dictionary of English v.0.48:

Carbon \Car"bon\ (k[aum]r"b[o^]n), n. [F. carbone, fr. L. carbo
   coal; cf. Skr. [,c]r[=a] to cook.] (Chem.)
   1. An elementary substance, not metallic in its nature, which
      is present in all organic compounds. Atomic weight 11.97.
      Symbol C. it is combustible, and forms the base of
      lampblack and charcoal, and enters largely into mineral
      coals. In its pure crystallized state it constitutes the
      diamond, the hardest of known substances, occuring in
      monometric crystals like the octahedron, etc. Another
      modification is graphite, or blacklead, and in this it is
      soft, and occurs in hexagonal prisms or tables. When
      united with oxygen it forms carbon dioxide, commonly
      called carbonic acid, or carbonic oxide, according to the
      proportions of the oxygen; when united with hydrogen, it
      forms various compounds called hydrocarbons. Compare
      Diamond, and Graphite.
      [1913 Webster]

   2. (Elec.) A carbon rod or pencil used in an arc lamp; also,
      a plate or piece of carbon used as one of the elements of
      a voltaic battery.
      [Webster 1913 Suppl.]

   3. a sheet of carbon paper.
      [PJC]

   4. a carbon copy.
      [PJC]

   Carbon compounds, Compounds of carbon (Chem.), those
      compounds consisting largely of carbon, commonly produced
      by animals and plants, and hence called organic compounds,
      though their synthesis may be effected in many cases in
      the laboratory.
      [1913 Webster]

            The formation of the compounds of carbon is not
            dependent upon the life process.      --I. Remsen

   carbon copy, originally, a copy of a document made by use
      of a carbon paper, but now used generally to refer to
      any copy of a document made by a mechanical process, such
      as xerographic copying.

   Carbon dioxide, Carbon monoxide. (Chem.) See under
      Carbonic.

   Carbon light (Elec.), an extremely brilliant electric light
      produced by passing a galvanic current through two carbon
      points kept constantly with their apexes neary in contact.


   Carbon point (Elec.), a small cylinder or bit of gas carbon
      moved forward by clockwork so that, as it is burned away
      by the electric current, it shall constantly maintain its
      proper relation to the opposing point.

   Carbon paper, a thin type of paper coated with a
      dark-colored waxy substance which can be transferred to
      another sheet of paper underneath it by pressing on the
      carbon paper. It is used by placing a sheet between two
      sheets of ordinary writing paper, and then writing or
      typing on the top sheet, by which process a copy of the
      writing or typing is transferred to the second sheet
      below, making a copy without the need for writing or
      typing a second time. Multiple sheets may be used, with a
      carbon paper placed above each plain paper to which an
      impression is to be transferred. In 1997 such paper was
      still used, particularly to make multiple copies of
      filled-in purchase invoice forms, but in most applications
      this technique has been superseded by the more faithful
      xerographic reproduction and computerized printing
      processes.

   Carbon tissue, paper coated with gelatine and pigment, used
      in the autotype process of photography. --Abney.

   Gas carbon, a compact variety of carbon obtained as an
      incrustation on the interior of gas retorts, and used for
      the manufacture of the carbon rods of pencils for the
      voltaic, arc, and for the plates of voltaic batteries,
      etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

carbon copy
    n 1: a copy made with carbon paper [syn: carbon, carbon
         copy]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "carbon copy":
   Doppelganger, actual thing, apograph, carbon, copy, dead ringer,
   ditto, double, duplicate, equivalent, exact counterpart, facsimile,
   fiche, homograph, homonym, homophone, idem, identical same,
   manifold, microcopy, microfiche, microform, no other, none other,
   recording, reduplication, replica, replication, rubbing, selfsame,
   spit and image, spitting image, synonym, tenor, the same,
   the same difference, tracing, transcript, transcription, transfer,
   twin, very image, very same