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.
This includes having a regular sleep schedule, avoiding caffeine in the afternoon and evening, exercising regularly, and keeping your bedroom cool and dark. — Alice Oglethorpe, Glamour, 2 Sep. 2026 Even drinking too much caffeine, which is a diuretic, can contribute. — Alexandra Frost, USA Today, 1 Sep. 2026 An herbal concoction of ginger, tea, mate, and eleuthero root, with a bit of citrus flavor and little to no caffeine, people drink it as a substitute for energy drinks or Gatorade. — Alaina Chou, Bon Appetit Magazine, 31 Aug. 2026 Short nights, dry cabin air, dehydration, alcohol, and caffeine all tip the body further towards fight-or-flight, leaving less room for recovery. — Anita Bhagwandas, Condé Nast Traveler, 31 Aug. 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 4 Sep. 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

Last Updated: - Updated example sentences
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