alkali

noun

1. (countable, uncountable)One of a class of caustic bases, such as soda, soda ash, caustic soda, potash, ammonia, and lithia, whose distinguishing characteristics are dissolving 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.

   “Alkalies may be defined as bodies which combine with acids so as to impair or neutralize their activity, and produce what are called salts. They are distinguished by properties the reverse of acids, and the two classes are generally looked upon as antagonist substances.”

2. (US, Western, countable, uncountable)Soluble mineral matter, other than common salt, contained in soils of natural waters.