Caffeine (noun)

1. A bitter alkaloid found in coffee, tea, and other plants, used as a stimulant.
2. A stimulant found in coffee, tea, and other plants, used to increase alertness and reduce fatigue.

Origin:

From french caféine, from café ("coffee") + -ine (from latin -īnus, suffix indicating chemical compounds).

Examples:

1. He needed caffeine to wake up.
2. She drank a cup of coffee for the caffeine.
3. The soda has caffeine in it.
4. The energy drink has high levels of caffeine.
5. The tea has less caffeine than coffee.