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

Too much caffeine can cause a racing heart, shakiness, anxiety, headaches, elevated blood pressure, and trouble sleeping. — Dr. Onaola Adedeji, ABC News, 13 Aug. 2026

Make sure to hydrate with water throughout the day, and avoid sugary beverages or drinks with caffeine which can affect your body's ability to cool off. — Jonathan Myers, CBS News, 12 Aug. 2026

Anyone who’s a serious caffeine enthusiast will enjoy this sleek stainless steel espresso machine with over 1,000 five-star reviews from Breville. — Kate McGregor, Architectural Digest, 11 Aug. 2026

Johns Hopkins advises 20 to 30 minutes of exercise each day, finished at least five to six hours before bed, and warns against caffeine, nicotine and alcohol, which disrupt normal sleep patterns. — Samantha Agate, Kansas City Star, 11 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