caffeine

[ka-feen, kaf-een, kaf-ee-in]
noun 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.
Also, caffein.


Origin:
1820–30; < French caféine, equivalent to café coffee + -ine -ine2

caffeinic [ka-fee-nik, kaf-ee-in-ik] , adjective
noncaffeine, noun
noncaffeinic, adjective
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
caffeine or caffein (ˈkæfiːn, ˈkæfɪˌiːn, ˈkæfiːn, ˈkæfɪˌiːn)
 
n
See also xanthine a white crystalline bitter alkaloid responsible for the stimulant action of tea, coffee, and cocoa: a constituent of many tonics and analgesics. Formula: C8H10N4O2
 
[C19: from German Kaffein, from Kaffeecoffee]
 
caffein or caffein
 
n
 
[C19: from German Kaffein, from Kaffeecoffee]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Etymonline
Word Origin & History

caffeine
1830, from Ger. Kaffein, coined by chemist F.F. Runge (1795-1867), apparently from Ger. Kaffee "coffee" + chemical suffix -ine (Ger. -in). The form of the English word may be via Fr. caféine.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

caffeine caf·feine or caf·fein (kā-fēn', kāf'ēn', kāf'ē-ĭn)
n.
A bitter white alkaloid often derived from tea or coffee and used chiefly as a mild stimulant and in the treatment of certain kinds of headache.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
caffeine   (kā-fēn')  Pronunciation Key 
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: C8H10N4O2.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
Caffeine is a substance that is found in certain plants.
Sometimes that requires a caffeine source or several sometimes that requires a
  trip to the gym.
It could be a close vote, but taxing caffeine has unfortunate precedents.
Alkaloids, which include caffeine and nicotine, are a highly diverse group of
  chemicals with many unusual properties.
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