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

Consume them in moderation, as too much caffeine can cause side effects. —Merve Ceylan, Health, 3 Dec. 2025

Powered by caffeine, hyaluronic acid, niacinamide, vitamin C, and collagen, Belif’s Aqua Bomb Eye Gel brightens, depuffs, hydrates, and smooths undereyes. —Lily Wohlner, Allure, 2 Dec. 2025

There are several ways to reduce your chances of having headaches, such as drinking plenty of water and limiting caffeine. —Katherine Cobb-Pitstick, The Conversation, 1 Dec. 2025

The couple were photographed heading to Vintage Coffee, taking photos with fans who stopped them on their pursuit of caffeine. —Anna Cafolla, Vogue, 30 Nov. 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