potash

noun

1. 1. potassium carbonate (esp. when obtained from wood ashes)
   2. potassium hydroxide
2. any substance containing potassium; esp., salts derived from natural brines, distillery waste, flue dusts of blast furnaces, etc., whose potassium content is expressed in terms of KO: used in fertilizers, soaps, etc.

Origin: earlier in pl., potashes < Du potasschen < pot, pot + asch, ash: orig. prepared by evaporating the lixivium of wood ashes in iron pots