Potash (?), 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).
[1913 Webster]