potash

From pot +‎ ash, because the substance was originally obtained by leaching ash in water and then boiling down the resulting solution in a pot.

Compare Saterland Frisian Potääske (“potash”), West Frisian potjiske (“potash”), Dutch potas (“potash”), Low German Pottasch, Puttasch (“potash”), German Pottasche (“potash”), Danish potaske (“potash”), Swedish potaska (“potash”), Icelandic pottaska (“potash”).