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).

• the water-soluble part of the ash formed by burning plant material; used for making soap, glass and as a fertilizer
  
• (chemistry) an impure form of potassium carbonate (K2CO3) mixed with other potassium salts
  
• (chemistry) (archaic) in the names of compounds of the form "... of potash", potassium (for example, "permanganate of potash" = potassium permanganate)