alkali

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A carbonate or hydroxide of an alkali metal, the aqueous solution of which is bitter, slippery, caustic, and characteristically basic in reactions.
• noun Any of various soluble mineral salts found in natural water and arid soils.
• noun Alkali metal.
• noun A substance having highly basic properties; a strong base.

from The Century Dictionary.

• noun This term, used in the commercial sense, includes the carbonates of sodium and potassium, formerly called mild alkalis, and the hydroxide of the same metals, the caustic alkalis. The alkali industry is one of great importance, especially the manufacture of soda, both carbonate and caustic. It is carried on mainly by three methods: the Leblanc process, the Solvay or ammonia process, and the electrolytic process. In the last of these, of recent introduction, a solution of common salt is decomposed by an electric current. The Solvay process is not practically applicable to the production of potash; it is at present the principal source of soda.
• noun Originally, the soluble part of the ashes of plants, especially of seaweed; soda-ash.
• noun The plant saltwort, Salsola kali. Also called kali.
• noun Now, any one of various substances which have the following properties in common: solubility in water; the power of neutralizing acids and forming salts with them; the property of combining with fats to form soaps; corrosive action on animal and vegetable tissue; the property of changing the tint of many vegetable coloring matters, as of litmus reddened by an acid to blue, or turmeric from yellow to brown.
• noun Sometimes spelled alcali.

from the GNU version of the Collaborative International Dictionary of English.

• noun Soda ash; caustic soda, caustic potash, etc.
• noun (Chem.) One of a class of caustic bases, such as soda, potash, ammonia, and lithia, whose distinguishing peculiarities are solubility in alcohol and water, uniting with oils and fats to form soap, neutralizing and forming salts with acids, turning to brown several vegetable yellows, and changing reddened litmus to blue.
• noun Western U. S. Soluble mineral matter, other than common salt, contained in soils of natural waters.
• noun potash and soda.
• noun Same as Alkaloids.
• noun ammonia, so called in distinction from the fixed alkalies.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry One of a class of caustic bases, such as soda, potash, ammonia, and lithia, whose distinguishing peculiarities are solubility in alcohol and water, uniting with oils and fats to form soap, neutralizing and forming salts with acids, turning to brown several vegetable yellows, and changing reddened litmus to blue.
• noun Soda ash; caustic soda, caustic potash, etc.
• noun Western United States Soluble mineral matter, other than common salt, contained in soils of natural waters.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of various water-soluble compounds capable of turning litmus blue and reacting with an acid to form a salt and water
• noun a mixture of soluble salts found in arid soils and some bodies of water; detrimental to agriculture