Nicotine n. : An alkaloid which is the active principle of tobacco. It is a colorless, transparent, oily liquid, having an acrid odor, and an acrid burning taste. It is intensely poisonous.

Example:
How much Nicotine do you get from smoking a cigarette?

Taxonomy
nicotine, the brain, PMID, risk, tobacco, schizophrenia, smokers, cigarettes, body, increases, dependence, 2006-11-06, Nicotine addiction, tobacco smoke, nicotinic receptors, sensitivity, nicotine gum, nicotinic acetylcholine receptors.

Defination from the web:
nicotine), the substance acts as a stimulant in mammals and is the main ... Nicotine is named after the tobacco plant Nicotiana tabacum, which in turn is named after Jean Nicot de Villemain, French ambassador in Portugal, ...