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

Brighten your undereye area and boost hydration with ingredients like vitamin C, caffeine, and honey. — Daley Quinn, Glamour, 9 July 2026

While no one wants a bad night's sleep, most of us experience occasional sleep disruptions stemming from familiar culprits like late-night doomscrolling, too much caffeine, stress or an inconsistent bedtime routine. — Daryl Austin, USA Today, 8 July 2026

With caffeine in hand, stroll to Davidson College’s Historic Quad to admire the Greek Revival architecture featured in landmarks like the columned Chambers Building (the center of academic life) and Philanthropic Hall (dating back to 1850). — Brennan Long, Southern Living, 7 July 2026

However, new research shows that moderate caffeine intake (around 250–300 mg per day) does not significantly increase urine output in people who regularly consume caffeine. — Sarah Jividen, Verywell Health, 7 July 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
• arene
• athene
• baleen
• beeline
• benzene
• between
• bromine

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