: 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
Dunkin’ has some seasonal options for fans who want to get in the spirit with a kick of caffeine.
—
Sabrina Weiss, PEOPLE, 29 Oct. 2025
The lack of sugar and caffeine hit me like a ton of bricks.
—Julia Gomez, USA Today, 29 Oct. 2025
Just be mindful of portion size and timing, as too much caffeine late in the day can disrupt sleep.
—Morgan Pearson, Verywell Health, 28 Oct. 2025
Research has shown that caffeine, the natural stimulant in coffee, may also improve workouts.
—Cynthia Sass, Health, 28 Oct. 2025
See All Example Sentences for caffeine
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Sabrina Weiss, PEOPLE, 29 Oct. 2025
The lack of sugar and caffeine hit me like a ton of bricks.
—Julia Gomez, USA Today, 29 Oct. 2025
Just be mindful of portion size and timing, as too much caffeine late in the day can disrupt sleep.
—Morgan Pearson, Verywell Health, 28 Oct. 2025
Research has shown that caffeine, the natural stimulant in coffee, may also improve workouts.
—Cynthia Sass, Health, 28 Oct. 2025
See All Example Sentences for caffeine
Cite this Entry
“Caffeine.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/caffeine. Accessed 3 Nov. 2025.
Copy CitationKids 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
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