The adjective alkaline, and less often, alkalescent, is commonly used in English as a synonym for basic, especially for bases soluble in water.
A water-extract of burned plant ashes, called potash and composed mostly of potassium carbonate, was mildly basic.
Caustic potash was traditionally used in conjunction with animal fats to produce soft soaps, one of the caustic processes that rendered soaps from fats in the process of saponification, one known since antiquity.
Alkalis are all Arrhenius bases, ones which form hydroxide ions (OH−) when dissolved in water.
Common properties of alkaline aqueous solutions include: The terms "base" and "alkali" are often used interchangeably, particularly outside the context of chemistry and chemical engineering.