\Pot"ash`\, n. [Pot + ash.] (Chem.)
(a) The hydroxide of potassium hydrate, a hard white brittle
    substance, {KOH}, having strong caustic and alkaline
    properties; -- hence called also {caustic potash}.
(b) The impure potassium carbonate obtained by leaching wood
    ashes, either as a strong solution (lye), or as a white
    crystalline (pearlash).