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 new Clear Protein Refreshers deliver 10 grams of protein, three grams of fiber, collagen, electrolytes, prebiotics, and 45 mg of caffeine for lasting nourishment and a light boost. — ABC News, 2 July 2026

Watch your caffeine intake, when drinking energy drinks that have more caffeine than coffee or tea. — Dinah Voyles Pulver, USA Today, 2 July 2026

Thanks to seven peptides, 13 brightening ingredients (like citric acid and caffeine), algae, ferulic acid, and teprenone. — Tamim Alnuweiri, InStyle, 2 July 2026

Avoiding alcohol and caffeine can also help your body maintain its internal temperature regulation. — Claire Cameron, Scientific American, 2 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