I. noun 1. a compound with particular chemical properties including turning litmus blue and neutralizing or effervescing with acids; typically, a caustic or corrosive substance of this kind such as lime or soda. • flint is not subject to chemical weathering except by strong alkalis.
• [ mass noun]
the reaction is followed by measuring the concentration of alkali at various times.
Often contrasted with acid and base1.
2. [as modifier] —
(chiefly N. Amer.) alkaline.Alkalis release hydroxide ions (OH−) when dissolved in water. Any solution with a pH of more than 7 is alkaline.
– origin late Middle English (denoting a saline substance derived from the ashes of various plants, including glasswort): from medieval Latin, from Arabic al-qalī ‘calcined ashes (of the glasswort etc.)’, from qalā ‘fry, roast’.