1 a any of a class of substances that liberate hydroxide ions in water, usu. form caustic or corrosive solutions, turn litmus blue, and have a pH of more than 7, e.g. caustic soda. b any other substance with similar but weaker properties, e.g. sodium carbonate.
2 Chem. any substance that reacts with or neutralizes hydrogen ions.
Phrases and idioms:
alkali metals any of the univalent group of metals, lithium, sodium, potassium, rubidium, and caesium, whose hydroxides are alkalis.
Derivatives:
alkalimeter n. alkalimetry n.
Etymology: ME f. med.L, f. Arab. al-kali calcined ashes f. kala fry
Useful english dictionary. 2012.