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

Mass spectrometry revealed that the broken containers had once held something containing the chemical compounds theobromine, theophylline, caffeine, and paraxanthine. — ArsTechnica, 27 Aug. 2026

King’s team identified staple cacao alkaloids (naturally occurring organic compounds with at least one nitrogen atom) including theobromine, theophylline, and caffeine on the shards. — Andrew Paul, Popular Science, 26 Aug. 2026

No one explicitly bans caffeine or alcohol, but after days of obsessing over my biomarkers, both begin to seem entirely irrelevant. — Abby Montanez, Robb Report, 23 Aug. 2026

Customers can pick their bases, flavors and even caffeine level. — Amelia Lucas, CNBC, 22 Aug. 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