Source : Webster's Revised Unabridged Dictionary (1913)

Tobacco \To*bac"co\, n. [Sp. tabaco, fr. the Indian tabaco the
   tube or pipe in which the Indians or Caribbees smoked this
   plant. Some derive the word from Tabaco, a province of
   Yucatan, where it was said to be first found by the
   Spaniards; others from the island of Tobago, one of the
   Caribbees. But these derivations are very doubtful.]
   1. (Bot.) An American plant ({Nicotiana Tabacum}) of the
      Nightshade family, much used for smoking and chewing, and
      as snuff. As a medicine, it is narcotic, emetic, and
      cathartic. Tobacco has a strong, peculiar smell, and an
      acrid taste.

   Note: The name is extended to other species of the genus, and
         to some unrelated plants, as Indian tobacco ({Nicotiana
         rustica}, and also {Lobelia inflata}), mountain tobacco
         ({Arnica montana}), and Shiraz tobacco ({Nicotiana
         Persica}).

   2. The leaves of the plant prepared for smoking, chewing,
      etc., by being dried, cured, and manufactured in various
      ways.

   {Tobacco box} (Zo["o]l.), the common American skate.

   {Tobacco camphor}. (Chem.) See {Nicotianine}.

   {Tobacco man}, a tobacconist. [R.]

   {Tobacco pipe}.
      (a) A pipe used for smoking, made of baked clay, wood, or
          other material.
      (b) (Bot.) Same as {Indian pipe}, under {Indian}.

   {Tobacco-pipe clay} (Min.), a species of clay used in making
      tobacco pipes; -- called also {cimolite}.

   {Tobacco-pipe fish}. (Zo["o]l.) See {Pipemouth}.

   {Tobacco stopper}, a small plug for pressing down the tobacco
      in a pipe as it is smoked.

   {Tobacco worm} (Zo["o]l.), the larva of a large hawk moth
      ({Sphinx, or Phlegethontius, Carolina}). It is dark green,
      with seven oblique white stripes bordered above with dark
      brown on each side of the body. It feeds upon the leaves
      of tobacco and tomato plants, and is often very injurious
      to the tobacco crop. See Illust. of {Hawk moth}.

Source : WordNet®

Nicotiana tabacum
     n : tall erect South American herb with large ovate leaves and
         terminal clusters of tubular white or pink flowers;
         cultivated for its leaves [syn: {common tobacco}]