: 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
Four Sigmatic is one of the OG mushroom coffees—one tablespoon delivers 9000mg of powerful adaptogenic mushroom powders like chaga, lion’s mane, and reishi, as well as a little caffeine (but less than your average cup of coffee).
—
Brianna Peters, Vogue, 2 Apr. 2026
Moderate caffeine, however, appears safe for most people if calcium intake is adequate.
—Hadia Zainab, CNN Money, 2 Apr. 2026
Lifestyle factors with solid evidence include a consistent sleep schedule, a protein-forward diet, resistance exercise and limiting afternoon caffeine and alcohol close to bedtime.
—Allison Palmer, Kansas City Star, 1 Apr. 2026
Lifestyle factors with real evidence behind them include a consistent sleep schedule, a protein-forward diet, resistance exercise and limiting afternoon caffeine and alcohol close to bedtime.
—Allison Palmer, Sacbee.com, 1 Apr. 2026
See All Example Sentences for caffeine
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Brianna Peters, Vogue, 2 Apr. 2026
Moderate caffeine, however, appears safe for most people if calcium intake is adequate.
—Hadia Zainab, CNN Money, 2 Apr. 2026
Lifestyle factors with solid evidence include a consistent sleep schedule, a protein-forward diet, resistance exercise and limiting afternoon caffeine and alcohol close to bedtime.
—Allison Palmer, Kansas City Star, 1 Apr. 2026
Lifestyle factors with real evidence behind them include a consistent sleep schedule, a protein-forward diet, resistance exercise and limiting afternoon caffeine and alcohol close to bedtime.
—Allison Palmer, Sacbee.com, 1 Apr. 2026
See All Example Sentences for caffeine
Cite this Entry
“Caffeine.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/caffeine. Accessed 5 Apr. 2026.
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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