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.
Doctors typically ask people to avoid caffeine and smoking beforehand because both raise the heart rate and blur the images. — Hanna Wickes, Kansas City Star, 20 Aug. 2026 Black tea has caffeine, is an appetite suppressant, promotes metabolism and is a common element in these teas. — Bestreviews, Chicago Tribune, 20 Aug. 2026 At the center is the brand’s proprietary Folligen Complex, which combines caffeine, biotin, peptides, and panthenol to care for both scalp and strands. — Christa Joanna Lee, Allure, 20 Aug. 2026 The tablets, which are a blend of the stimulant with caffeine and other adulterants, are particularly common in South and Southeast Asia. — Chas Newkey-Burden, TheWeek, 18 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 25 Aug. 2026.

Copy Citation

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
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

More from Merriam-Webster

Word of the Day

Listen to the pronunciation of tilde

See Definitions and Examples »

Popular in Grammar & Usage

See More

A Who’s Who Regarding ‘Who’s’ and ‘Whose’

How to Pronounce the Trickiest Menu Items

Is that lie 'bald-faced' or 'bold-faced'?

'A' or 'an'? What about before 'h'? An Indefinite Article Guide

Why is '-ed' sometimes pronounced at the end of a word?
See More

Popular in Wordplay

See More

Words from the 'Odyssey'

The Longest Long Words List

Even More Words That Sound Like Insults But Aren't

The Words of the Week - Aug. 21

16 Glee-ridden Words from Schitt's Creek
See More

Popular

See More

A Who’s Who Regarding ‘Who’s’ and ‘Whose’

Words from the 'Odyssey'

The Longest Long Words List
See More

Games & Quizzes

See All
Play Quordle: Guess all four words in a limited number of tries. Each of your guesses must be a real 5-letter word.
Quordle Can you solve 4 words at once?
Play Blossom: Solve today's spelling word game by finding as many words as you can using just 7 letters. Longer words score more points.
Blossom Pick the best words!
Play Missing Letter: a crossword with a twist. Each of the 25 puzzle words start with a different letter of the alphabet. Which letter is missing?
The Missing Letter A daily crossword with a twist
alt-684346df967d5
Add A Letter Quiz Pick the letter that goes in the same spot in fou...
See All