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

This may be because coffee contains other compounds with antioxidant and anti-inflammatory properties that may counterbalance caffeine’s downsides over time. —Kathleen Ferraro, Verywell Health, 5 Mar. 2026

To ease the transition, experts recommend adjusting sleep schedules gradually, limiting caffeine intake, and using light exposure strategically to help the body adapt to the new time. —Miami Herald Archives, Miami Herald, 5 Mar. 2026

Both drinks hydrate and are very low in calories, but green tea offers more potent antioxidants, while lemon water provides vitamin C without caffeine. —Lindsey Desoto, Health, 5 Mar. 2026

For a standard cup of coffee, avoid caffeine within 4 hours of bedtime. —Allison Palmer march 4, Charlotte Observer, 4 Mar. 2026

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