Alkaline \Al"ka*line\ (?; 277), a. [Cf. F. alcalin.] Of or pertaining to an alkali or to alkalies; having the properties of an alkali. {Alkaline earths}, certain substances, as lime, baryta, strontia, and magnesia, possessing some of the qualities of alkalies. {Alkaline metals}, potassium, sodium, c[ae]sium, lithium, rubidium. {Alkaline reaction}, a reaction indicating alkalinity, as by the action on limits, turmeric, etc.