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

And obviously, caffeine is a big part of it, and just doing things. —Kayla Grant, PEOPLE, 9 Sep. 2025

Avoid caffeine or stimulants at least eight hours before bedtime. —Rosanna Sutherby, Verywell Health, 9 Sep. 2025

Specifically, caffeine causes the kidneys to filter more fluid, prevents them from reabsorbing normal amounts of sodium, and can even disrupt certain signals between the liver and kidneys, Gentile told Health. —Fran Kritz, Health, 9 Sep. 2025

This is a jolt of exciting news for Boise-area caffeine fiends. —Michael Deeds, Idaho Statesman, 8 Sep. 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