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Showing results for caffeine. Search instead for Caffeic.
Synonyms

caffeine

American  
[ka-feen, kaf-een, kaf-ee-in] / kæˈfin, ˈkæf in, ˈkæf i ɪn /
Rarely caffein

noun

  1. Chemistry, Pharmacology. a white, crystalline, bitter alkaloid, C 8 H 10 N 4 O 2 , usually derived from coffee or tea: used in medicine chiefly as a nervous system stimulant.

  2. Informal. a drink, usually coffee or tea, containing this stimulant.

    We sipped our caffeine on the balcony with its views of sea stacks, rocky coves, and the ever-changing ocean.
caffeine British  
/ ˈkæfiːn, ˈkæfɪˌiːn /

noun

  1. a white crystalline bitter alkaloid responsible for the stimulant action of tea, coffee, and cocoa: a constituent of many tonics and analgesics. Formula: C 8 H 10 N 4 O 2 See also xanthine

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
caffeine Scientific  
/ kă-fēn′ /

  1. A bitter white alkaloid found in tea leaves, coffee beans, and various other plant parts. It is a mild stimulant. Caffeine is a xanthine and similar in structure to theobromine and theophylline. Chemical formula: C 8 H 10 N 4 O 2 .

Other Word Forms

  • caffeinic adjective
  • noncaffeine noun
  • noncaffeinic adjective

Etymology

Origin of caffeine

First recorded in 1820–30; from French caféine, equivalent to café coffee + -ine -ine 2

Compare meaning

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Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

"We found that flies consuming caffeine at night were less able to suppress movement, displaying impulsive behaviors such as reckless flying despite these aversive conditions."

From Science Daily • Mar. 31, 2026

Kirkland Signature energy drinks mimic Celsius’s look, flavors, and 200 milligrams of caffeine, causing Celsius shares to fall.

From The Wall Street Journal • Mar. 25, 2026

It was a group powered by caffeine, Johnston said, and their coffee came in handy when they needed a liquid prop to do quick demos with the prototypes to test their absorbency.

From The Wall Street Journal • Mar. 20, 2026

This suggests that caffeine may be an important factor behind the observed brain-related benefits, although more research is needed to confirm the underlying mechanisms.

From Science Daily • Mar. 18, 2026

Judging from his dilated eyes and his maniacal grin, he didn’t need any more caffeine.

From "The House of Hades" by Rick Riordan

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.