caf·​feine | \ ka-ˈfēn, ˈka-ˌfēn\

Definition of caffeine

: a bitter alkaloid C8H10N4O2 found especially in coffee, tea, cacao, and kola nuts and used medicinally as a stimulant and diuretic

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Examples of caffeine in a Sentence

Her doctor told her to avoid caffeine.

Recent Examples on the Web

The latest wave of products pack a host of depuffing, fine-line–plumping actives, from caffeine and rejuvenating black pearl to 24-karat gold. Zoe Ruffner, Vogue, "9 Under-Eye Masks to Banish Puffiness Once and for All," 28 Dec. 2018 For those who cannot stomach milky drinks, stick with something between 98.6 and 115 degrees, with no caffeine. Heidi Mitchell, WSJ, "How Much Do Hot Drinks Help on a Cold Day?," 5 Dec. 2018 Whether athletes can enhance their performance with caffeine may depend on their genes. Gretchen Reynolds, New York Times, "Can Coffee Rev Up Your Workout? It May Depend on Your Genes," 21 Mar. 2018 There’s laid-back Portland, Oregon, with its innovative brew scene, or Seattle, where the invention of Starbucks kicked off a long-standing relationship with caffeine. Cassie Shortsleeve, Condé Nast Traveler, "The 10 Best Coffee Cities in the U.S.," 15 Jan. 2018 The bottle was tested, revealing trace amounts of acetaminophen (a pain reliever and fever reducer), caffeine and aspirin. Chris Harris,, "Teen Admits She Tried to Kill Her Newborn Niece by Lacing Breast Milk With Pain Pills," 14 Mar. 2018 Out comes soluble solids like caffeine and sugars, and the gases that give it that life-affirming smell. Alexander George, Popular Mechanics, "This Video Explains the Science of Perfect Espresso," 10 Apr. 2015 Use the guideline of 400 milligrams of caffeine per day as your max, which is the equivalent of Venti at Starbucks, and time this accordingly. Jaclyn London, Ms, Rd, Cdn, Good Housekeeping, "How to Start Losing Weight With 6 Steps That Actually Work, According to a Nutritionist," 5 Dec. 2018 Coca-Cola was forced to cut the amount of caffeine in the beverage by half and pay all court costs. Jennifer Ouellette, Ars Technica, "We have food safety laws thanks to 19th century “poison squad”," 26 Nov. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'caffeine.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of caffeine

circa 1823, in the meaning defined above

History and Etymology for caffeine

German Kaffein, from Kaffee coffee, from French café

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Statistics for caffeine

Last Updated

14 Jan 2019

Look-up Popularity

Time Traveler for caffeine

The first known use of caffeine was circa 1823

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More Definitions for caffeine



English Language Learners Definition of caffeine

: a substance that is found especially in coffee and tea and that makes you feel more awake


caf·​feine | \ ka-ˈfēn, ˈka-ˌfēn\

Kids Definition of caffeine

: a substance found especially in coffee and tea that makes a person feel more awake


caf·​feine | \ ka-ˈfēn, ˈka-ˌ; ˈkaf-ē-ən \

Medical Definition of caffeine

: a bitter alkaloid C8H10N4O2 found especially in coffee, tea, and kola nuts and used medicinally as a stimulant and diuretic

Other Words from caffeine

caffeinic \ ka-​ˈfē-​nik , ˌkaf-​ē-​ˈin-​ik \ adjective

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More from Merriam-Webster on caffeine

Rhyming Dictionary: Words that rhyme with caffeine

Spanish Central: Translation of caffeine

Nglish: Translation of caffeine for Spanish Speakers

Britannica English: Translation of caffeine for Arabic Speakers Encyclopedia article about caffeine

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