Source : Webster's Revised Unabridged Dictionary (1913)

Tar \Tar\, n. [OE. terre, tarre, AS. teru, teoru; akin to D.
   teer, G. teer, theer, Icel. tjara, Sw. tj["a]ra, Dan.
   ti[ae]re, and to E. tree. [root]63. See {Tree}.]
   A thick, black, viscous liquid obtained by the distillation
   of wood, coal, etc., and having a varied composition
   according to the temperature and material employed in
   obtaining it.

   {Coal tar}. See in the Vocabulary.

   {Mineral tar} (Min.), a kind of soft native bitumen.

   {Tar board}, a strong quality of millboard made from junk and
      old tarred rope. --Knight.

   {Tar water}.
   (a) A cold infusion of tar in water, used as a medicine.
   (b) The ammoniacal water of gas works.

   {Wood tar}, tar obtained from wood. It is usually obtained by
      the distillation of the wood of the pine, spruce, or fir,
      and is used in varnishes, cements, and to render ropes,
      oakum, etc., impervious to water.

Coal \Coal\, n. [AS. col; akin to D. kool, OHG. chol, cholo, G.
   kohle, Icel. kol, pl., Sw. kol, Dan. kul; cf. Skr. jval to
   burn. Cf. {Kiln}, {Collier}.]
   1. A thoroughly charred, and extinguished or still ignited,
      fragment from wood or other combustible substance;
      charcoal.

   2. (Min.) A black, or brownish black, solid, combustible
      substance, dug from beds or veins in the earth to be used
      for fuel, and consisting, like charcoal, mainly of carbon,
      but more compact, and often affording, when heated, a
      large amount of volatile matter.

   Note: This word is often used adjectively, or as the first
         part of self-explaining compounds; as, coal-black; coal
         formation; coal scuttle; coal ship. etc.

   Note: In England the plural coals is used, for the broken
         mineral coal burned in grates, etc.; as, to put coals
         on the fire. In the United States the singular in a
         collective sense is the customary usage; as, a hod of
         coal.

   {Age of coal plants}. See {Age of Acrogens}, under {Acrogen}.
      

   {Anthracite} or {Glance coal}. See {Anthracite}.

   {Bituminous coal}. See under {Bituminous}.

   {Blind coal}. See under {Blind}.

   {Brown coal}, or {Lignite}. See {Lignite}.

   {Caking coal}, a bituminous coal, which softens and becomes
      pasty or semi-viscid when heated. On increasing the heat,
      the volatile products are driven off, and a coherent,
      grayish black, cellular mass of coke is left.

   {Cannel coal}, a very compact bituminous coal, of fine
      texture and dull luster. See {Cannel coal}.

   {Coal bed} (Geol.), a layer or stratum of mineral coal.

   {Coal breaker}, a structure including machines and machinery
      adapted for crushing, cleansing, and assorting coal.

   {Coal field} (Geol.), a region in which deposits of coal
      occur. Such regions have often a basinlike structure, and
      are hence called {coal basins}. See {Basin}.

   {Coal gas}, a variety of carbureted hydrogen, procured from
      bituminous coal, used in lighting streets, houses, etc.,
      and for cooking and heating.

   {Coal heaver}, a man employed in carrying coal, and esp. in
      putting it in, and discharging it from, ships.

   {Coal measures}. (Geol.)
      (a) Strata of coal with the attendant rocks.
      (b) A subdivision of the carboniferous formation, between
          the millstone grit below and the Permian formation
          above, and including nearly all the workable coal beds
          of the world.

   {Coal oil}, a general name for mineral oils; petroleum.

   {Coal plant} (Geol.), one of the remains or impressions of
      plants found in the strata of the coal formation.

   {Coal tar}. See in the Vocabulary.

   {To haul over the coals}, to call to account; to scold or
      censure. [Colloq.]

   {Wood coal}. See {Lignite}.

Coal tar \Coal" tar`\
   A thick, black, tarry liquid, obtained by the distillation of
   bituminous coal in the manufacture of illuminating gas; used
   for making printer's ink, black varnish, etc. It is a complex
   mixture from which many substances have been obtained,
   especially hydrocarbons of the benzene or aromatic series.

   Note: Among its important ingredients are benzene, aniline,
         phenol, naphtalene, anthracene, etc., which are
         respectively typical of many dye stuffs, as the aniline
         dyes, the phthale["i]ns, indigo, alizarin, and many
         flavoring extracts whose artificial production is a
         matter of great commercial importance.

Source : WordNet®

coal tar
     n : a tar formed from distillation of bituminous coal; coal tar
         can be further distilled to give various aromatic
         compounds