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

Sleep researchers explain the impact of diet, caffeine and alcohol on sleep health and share a list of sleep-supporting foods. —Malaka Gharib, NPR, 10 Dec. 2025

Get your caffeine fix at this small-batch artisan roaster that donates a portion of its sales to go toward open space and wildlife conservation. —Nicole Kliest, Vogue, 10 Dec. 2025

They are soaked in an effective and nourishing blend of caffeine, kojic acid, and arbutin to even discoloration and hydrate the thin area of skin. —Olivia Dubyak, Travel + Leisure, 9 Dec. 2025

At that point, the caffeine is released gradually, supporting a more stable, longer-lasting buzz without an afternoon crash, Fritsche says. —Matt Fuchs, Time, 8 Dec. 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