caffeine

noun

caf·​feine ka-ˈfēn 

ˈka-ˌfēn

: a bitter alkaloid C₈H₁₀N₄O₂ found especially in coffee, tea, cacao, and kola nuts and used medicinally as a stimulant and diuretic

Examples of caffeine in a Sentence

Her doctor told her to avoid caffeine.

Recent Examples on the Web

My brother was a poet, classics scholar, and charismatic leader of nerds who blossomed into a handsome surfer and then nosedived into schizophrenia and a life of unfiltered Camel cigarettes, caffeine, and antipsychotics. —Kim Gordon, Rolling Stone, 3 Sep. 2025

Psychology professor Anu Realo of the University of Warwick said the positive effects happen after caffeine blocks adenosine receptors in the brain. —Andrea Margolis, FOXNews.com, 29 Aug. 2025

The Slow Burn of Modern Taste Low-caf is not just a compromise for caffeine-intolerant souls. —Lyssanoel Frater, USA Today, 28 Aug. 2025

Keep in mind that caffeine content can vary by bean and brewing method. —Ashley Olivine, Verywell Health, 28 Aug. 2025

Word History

Etymology

German Kaffein, from Kaffee coffee, from French café

First Known Use

circa 1823, in the meaning defined above

Phrases Containing caffeine

• caffeine-free

Rhymes for caffeine

• agin
• alkene
• allene
• ameen
• amin
• amine
• arene
• athene
• baleen
• beeline
• benzene
• between

Kids Definition

caffeine

noun

caf·​feine ka-ˈfēn 

ˈka-ˌfēn

: a bitter stimulating compound found especially in coffee, tea, cacao, and kola nuts

Medical Definition

caffeine

noun

caf·​feine ka-ˈfēn, ˈka-ˌ; ˈkaf-ē-ən 

: a bitter alkaloid C₈H₁₀N₄O₂ found especially in coffee, tea, and kola nuts and used medicinally as a stimulant and diuretic

caffeinic

ka-ˈfē-nik  ˌkaf-ē-ˈin-ik 

adjective