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Chemistry.

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.
any of various other more or less active bases, as calcium hydroxide.
(not in technical use) an .
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, .
Historical Examples

A man would die of alkali in this place before he’s waited on.
Hopalong Cassidy Clarence E. Mulford

The day had been long, and the alkali lay light on the desert.
Whispering Smith Frank H. Spearman

The soda carbonate may also be added to soap as a solution of soda ash (58° alkali) either concentrated, 62° Tw.
The Handbook of Soap Manufacture W. H. Simmons

His face was yellowing again, under the blister of sun and alkali.
Warrior Gap Charles King

It dissolves in an excess of alkali to form plumbites of the general formula Pb(OM)2.
Encyclopaedia Britannica, 11th Edition, Volume 16, Slice 3 Various

Neither did I put any sal-soda, or other acid or alkali, into my bread.
Walden, and On The Duty Of Civil Disobedience Henry David Thoreau

Lemonades an acid, and it needs an alkali to take it out, declared Frank.
For the Honor of Randall Lester Chadwick

An alkali procured by burning Salsola kali and other sea-shore plants.
The Sailor’s Word-Book William Henry Smyth

Iron is precipitated from this solution by the Prussian alkali.
Heads of Lectures on a Course of Experimental Philosophy: Particularly Including Chemistry Joseph Priestley

Water removes the whole of the alkali, but alcohol only removes one half.
The Dyeing of Cotton Fabrics Franklin Beech

noun (pl) -lis, -lies
(chem) a soluble base or a solution of a base
a soluble mineral salt that occurs in arid soils and some natural waters
n.

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.

alkali al·ka·li (āl’kə-lī’)
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.

alkali
(āl’kə-lī’)
Plural alkalis or alkalies
A hydroxide of an alkali metal. The aqueous solution of alkalis is bitter, slippery, caustic, and characteristically basic in reactions.
alkali [(al-kuh-leye)]

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

Note: Plants have difficulty growing in soil that is rich in alkalis.