caffeine

noun

caf·​feine ka-ˈfēn How to pronounce caffeine (audio)
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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Cheng told Hackensack Meridian Health that drinking caffeine during this window can temporarily raise cortisol even further, potentially contributing to feelings of anxiety or restlessness. — Hanna Wickes, Kansas City Star, 15 Oct. 2026 How caffeine actually works in your body Caffeine’s real job is receptor blockade. — Hanna Wickes, Charlotte Observer, 15 Oct. 2026 Adding caffeine, which mops up radicals, largely stopped the clumping, pointing to the radicals as the cause. — Jacek Krywko, ArsTechnica, 15 Oct. 2026 For a caffeine fix paired with handmade confections, indulge in the Dolce Vita Afternoon Tea on weekends. — Condé Nast, Condé Nast Traveler, 13 Oct. 2026 See All Example Sentences for caffeine

Word History

Etymology

German Kaffein, from Kaffee coffee, from French café

First Known Use

circa 1823, in the meaning defined above

Time Traveler
The first known use of caffeine was circa 1823

Phrases Containing caffeine

Rhymes for caffeine

See All Rhymes for caffeine

Browse Nearby Words

caffeinated
caffeine
caffeine citrate
See all Nearby Words

Cite this Entry

“Caffeine.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/caffeine. Accessed 20 Oct. 2026.

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Kids Definition

caffeine

noun
caf·​feine ka-ˈfēn How to pronounce caffeine (audio)
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 How to pronounce caffeine (audio)
: a bitter alkaloid C8H10N4O2 found especially in coffee, tea, and kola nuts and used medicinally as a stimulant and diuretic
caffeinic
ka-ˈfē-nik How to pronounce caffeine (audio) ˌkaf-ē-ˈin-ik How to pronounce caffeine (audio)
adjective

More from Merriam-Webster on caffeine

Britannica.com: Encyclopedia article about caffeine

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