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

Some tips for improving sleep include having a regular routine/bedtime, sleeping in a cool room, limiting alcohol and caffeine, getting regular exercise, and avoiding devices such as cell phones and tablets before bed. —Allison Futterman, Discover Magazine, 13 Feb. 2025

Screen time and caffeine should be avoided in the hours leading up to sleep. —Arielle Tschinkel, Parents, 12 Feb. 2025

Now that your energy is up from the caffeine and food, walk back toward the hotel to get on the Swamp Rabbit Trail. —Alexandra Maloney, Charlotte Observer, 10 Feb. 2025

In addition, limit caffeine and alcohol, both of which may constrict blood vessels and worsen Raynaud’s, Dr. Kahaleh says. —Cindy Kuzma, SELF, 6 Feb. 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

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