The word 'tobacco' is reported to derive from the Spanish 'tobaca' -a term used by the Spanish to describe a Y-shped instrument used by early American Indians to inhale snuff of various types into the nostrils.
Tobacco(picatt) was used by the early American Indians to relieve toothache,to treat skin wound and insect bites,as an antifague agent and as a tooth whitening agent.
Tobacco is used to manufacture the various forms of smoking tobacco,chewing tobacco and tobacco and tobacco snuff is chiefly derived from two species of the plant genus Nicotiana.The two speces are N.tabacum and N.rustica.The addictive property of tobacco is due to one of its component alkaloids,nicotine.Raw and processed tobacco has been shown to contain over 2500 different chemical constituents.

Composition:
Tobacco contains a variety of different chemical of these constituents ,tobacco specific N-nitrosa are the compounds which are thought to be the major Carcinogenic agents in tobacco.
Non-volatile N-nitrosa compounds include N-nitrosonornicotine(NNN),& -(methylnetro-samino),(3 pyridifl), butanone(NNK) and N-nitroso -anatabine(NAT)
The non-volatile N-nitrosa compound are derived from tobacco alkaloids.the a;lkalcid nicotine can give rise toNNN,NNk and NAT although NNN can also derive from the alkaloid nornicotine and NAT from the alkaloid autsbine.Other nitresamines are also found in the processed tobacco.