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

At almost any hour, someone is settling in for a caffeine fix, a glass of wine, or one more dirty martini. — Condé Nast, Condé Nast Traveler, 29 Sep. 2026

For a morning caffeine fix, Hatchet West and Bohemia Coffee House are solid downtown options that make good starting points for a day of exploring. — Kristy Tolley, Travel + Leisure, 26 Sep. 2026

Also contributing to a balanced scalp is caffeine, which stimulates the scalp skin and, with continuous use, potentially encourages growth. — Sarah Han, Allure, 24 Sep. 2026

Thanks to the high concentration of PDRN, niacinamide, NAD, and caffeine, the mask has all of the right ingredients to moisturize, firm, and revitalize your skin in one use. — Essence Wiley, InStyle, 24 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