Nicotin is a drug found in tobacco. It is what makes people want to smoke.
Nicotin is usually thought of as a bad thing because it can be harmful to people's health.
Examples:
Many people are addicted to nicotin.
My uncle smokes a lot of nicotin.
Nicotin is in cigarettes.
I don't want to be near people who use nicotin.
Some people say nicotin is as addictive as heroin.
Nicotin is very bad for you, so you should never use it.