Nic·o·tine n.  Chem. An alkaloid which is the active principle of tobacco (C10H14N2).  It occurs in tobacco plants (Nicotiana tabacum and Nicotiana rusticum) to the extent of 2 to 8%, in combination with malic acid or citric acid.  It is a colorless, transparent, oily liquid, having an acrid odor, and an acrid burning taste.  It is intensely poisonous.  The apparently addictive effects of tobacco smoking have been ascribed largely to the effect of nicotine, and the controlled administration of nicotine on various forms has been used as a technique for assisting efforts to stop the smoking habit.

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 To·bac·co n.
 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 Zool., 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. Zool. See Pipemouth.
 Tobacco stopper, a small plug for pressing down the tobacco in a pipe as it is smoked.
 Tobacco worm Zool., the larva of a large hawk moth (Sphinx Carolina syn. 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.

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 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]