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

The research, published in the scientific journal Microbial Cell, examined the effect of caffeine on fission yeast cells. — Maggie Ryan, Flow Space, 21 Sep. 2026

Beyond tea, which provides caffeine, an entirely different nonalcoholic category introduces naturally occurring ingredients that cause various mood-altering effects. — Esther Tseng, Bon Appetit Magazine, 21 Sep. 2026

Hyaluronic acid hydrates and plumps the delicate undereye area, caffeine visibly reduces puffiness, and soothing aloe leaf and antioxidant-rich green tea keep skin looking calm, smooth, and radiant. — Christa Joanna Lee, Allure, 18 Sep. 2026

Avoid foods and drinks that may worsen reflux, including alcohol, caffeine, chocolate and mint. — Melissa Rudy, FOXNews.com, 18 Sep. 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