another name for potassium carbonate, esp the form obtained by leaching wood ash
C17 pot ashes, translation of obsolete Dutch potaschen; so called because originally obtained by evaporating the lye of wood ashes in pots
Potash has been used for centuries in the manufacture of glass and soap and as a fertilizer. It was made by burning hardwood and soaking the ashes in water, which created lye. Lye was then baked down into "black ashes" or potash. Today, potash is primarily mined and used in inorganic fertilizer.
I got curious about this word when I heard it in this morning's news. Link for the curious.