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

Home bakers wanting to avoid caffeine can simply swap in decaf coffee; the switch does not noticeably affect the flavor. —The Washington Post, San Diego Union-Tribune, 21 Jan. 2026

This is a gradual self-tanning lotion that helps reduce the appearance of cellulite with ingredients such as collagen, elastin and caffeine from green tea. —Bestreviews, Chicago Tribune, 21 Jan. 2026

Experts say the caffeine and scent levels in used grounds are too weak to deter bugs effectively. —Lauren Landers, The Spruce, 21 Jan. 2026

Additionally, taking pre-workout around the same time as other caffeine sources can increase the risk of these side effects. —Morgan Pearson, Verywell Health, 21 Jan. 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
• 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