caffeine

n. vegetable alkaloid found in coffee and tea plants, stimulant

Caffeine is a xanthine alkaloid compound that acts as a psychoactive stimulant in humans. The word comes from the French term for coffee, café. Caffeine is also called guaranine when found in guarana, mateine when found in mate, and theine when found in tea; all these names are considered chemical synonyms for the same chemical compound.
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Caffeine is a drug that stimulates the central nervous system. Purpose Caffeine makes people more alert, less drowsy, and [more]Caffeine - Community and Resources

Noun
1. a bitter alkaloid found in coffee and tea that is responsible for their stimulating effects
(synonym) caffein
(hypernym) alkaloid
(substance-holonym) coffee, java

(n.)
A white, bitter, crystallizable substance, obtained from coffee. It is identical with the alkaloid theine from tea leaves, and with guaranine from guarana.