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

Another habit linked to adenosine receptors and sleep quality is stopping your caffeine in the early afternoon. —Tanya Akim, Forbes, 10 Mar. 2025

Avoid drinking caffeine, alcohol or eating a big meal at least two hours before bedtime. —Lauryn Higgins, Flow Space, 10 Mar. 2025

And cut out the afternoon coffees — caffeine has a long half life and can still be in your system by bedtime. —Sarah Boden, NPR, 9 Mar. 2025

The caffeine in green coffee bean extract is a natural stimulant, which, on its own or when combined with other stimulants, can have negative health consequences. —Allison Herries, Verywell Health, 7 Mar. 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