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

Typically, carbonated options dominate the energy drink aisle, allowing Celsius to stand out and win over customers who might otherwise stick to tea or coffee for their caffeine fix. —Amelia Lucas, CNBC, 24 May 2026

The caffeine in this eye cream did not take long to get to work. —Tamim Alnuweiri, InStyle, 23 May 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, 22 May 2026

Hojicha has many of the same benefits as matcha but with much less caffeine. —Irenie Forshaw, TheWeek, 22 May 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