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

Consuming caffeine relaxes the muscular valve between the esophagus and stomach, according to the Cleveland Clinic, which can cause stomach acid to move up into the esophagus and possibly lead to heartburn. — Sadie Chafe, FOXNews.com, 2 Nov. 2026

Speaking of actives, the formula is also fortified with a triple peptide blend to tighten and firm, kakadu plum and caffeine extract to brighten, and marine extracts to target crepiness. — Lauren Valenti, Vogue, 29 Oct. 2026

Rushing to your appointment, feeling anxious, or drinking caffeine can raise your blood pressure. — Brandi Jones, Verywell Health, 29 Oct. 2026

Chocolate also contains caffeine itself, which can have the same effects. — Adam Harrington, CBS News, 28 Oct. 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