Nicotine is a drug that's present in tobacco. People who are addicted to cigarettes are really hooked on nicotine.
Nicotine is most commonly known for occurring in tobacco, and therefore in cigarettes. In small amounts, nicotine is a stimulant, although in larger quantities it's considered a poison and is even used in many insecticides. The earliest French root of the word was nicotiane, which comes from the Modern Latin botanical term for the tobacco plant, Nicotiana, named for Jean Nicot, the French ambassador who first brought tobacco from Brazil to France in 1561.