noun, plural al·ka·lis, al·ka·lies.

  1. any of various bases, the hydroxides of the alkali metals and of ammonium, that neutralize acids to form salts and turn red litmus paper blue.
  2. any of various other more or less active bases, as calcium hydroxide.
  3. (not in technical use) an alkali metal.
  4. Obsolete.any of various other compounds, as the carbonates of sodium and potassium.
Agriculture. a soluble mineral salt or a mixture of soluble salts, present in some soils, especially in arid regions, and detrimental to the growing of most crops.


Chemistry. alkaline.


Origin of alkali

1300–50; Middle English alkaly < Middle French alcali < dialectal Arabic al-qalī, variant of Arabic qily saltwort ashes Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for alkali

Historical Examples of alkali

  • The microscopic test of the distribution of alkali in the blood.

  • The day had been long, and the alkali lay light on the desert.

    Whispering Smith

    Frank H. Spearman

  • Be ready to tie your neckerchief over your nose, soon as we strike the alkali.

    Bloom of Cactus

    Robert Ames Bennet

  • Wonder if she would have any use for a maverick rancher from the alkali 174 country?

    The Pirate of Panama

    William MacLeod Raine

  • A determination of alkali therefore determines the percentage of cellulose.

British Dictionary definitions for alkali


noun plural -lis or -lies

chem a soluble base or a solution of a base
a soluble mineral salt that occurs in arid soils and some natural waters

Word Origin for alkali

C14: from Medieval Latin, from Arabic al-qili the ashes (of the plant saltwort)
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

Word Origin and History for alkali

late 14c., "soda ash," from Medieval Latin alkali, from Arabic al-qaliy "the ashes, burnt ashes" (of saltwort, a plant growing in alkaline soils), from qala "to roast in a pan." The modern chemistry sense is from 1813.

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for alkali



n. pl. al•ka•lis

A carbonate or hydroxide of an alkali metal, the aqueous solution of which is bitter, slippery, caustic, and characteristically basic in reactions.
Any of various soluble mineral salts found in natural water and arid soils.
Alkali metal.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for alkali



Plural alkalis alkalies

A hydroxide of an alkali metal. The aqueous solution of alkalis is bitter, slippery, caustic, and characteristically basic in reactions.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Culture definitions for alkali



A bitter, caustic mineral often found in large beds in the desert. Alkalis are bases; two common examples are lye and ammonia.


Plants have difficulty growing in soil that is rich in alkalis.
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.