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

By cutting the amount of coffee in half and replacing it with natural ingredients, the drinker receives a milder caffeine boost and supplemental benefits from the mushrooms. —Bestreviews, Chicago Tribune, 13 Aug. 2025

Throughout the process, Tiafoe was along for testing the caffeine usage and levels, the flavor profiles and even the bar’s packaging. —Tim Newcomb, Forbes.com, 13 Aug. 2025

Contrary to popular belief, though, Red Bull isn't Dew's favorite caffeine source. —Rachel Raposas, People.com, 13 Aug. 2025

Coffee was available 24/7, said Preller, who drank beverages without caffeine. —Tom Krasovic, San Diego Union-Tribune, 12 Aug. 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