alkali (ălˈkəlĪ) [key] [Arab., al-gili = ashes of saltwort], hydroxide of an alkali metal. Alkalies are readily soluble in water and form strongly basic solutions with a characteristic acrid taste. They neutralize acids, forming salts and water. Strong alkalies (e.g., those of sodium or potassium) are sometimes called caustic alkalies. The term alkali originally applied to salts obtained from plant ashes and is sometimes applied to a carbonate of sodium or potassium or to the hydroxide of an alkaline-earth metal.