noun, plural al·ka·lis, al·ka·lies.

  1. Chemistry.
    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.
  2. 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.


  1. Chemistry. alkaline.

noun plural -lis or -lies

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

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.

n. pl. al•ka•lis

  1. A carbonate or hydroxide of an alkali metal, the aqueous solution of which is bitter, slippery, caustic, and characteristically basic in reactions.
  2. Any of various soluble mineral salts found in natural water and arid soils.
  3. Alkali metal.

Plural alkalis alkalies

  1. A hydroxide of an alkali metal. The aqueous solution of alkalis is bitter, slippery, caustic, and characteristically basic in reactions.

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

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