potash

Short definition from Wiktionary

Noun

1. 1
   The water-soluble part of wood ash, used for making soap and glass and as a fertilizer (chemically speaking, an impure form of potassium carbonate (K₂CO₃) mixed with other potassium salts).
2. 2
   Potassium. Chiefly used in the names of compounds of the form "... of potash".
3. 3
   A class of potassium minerals, of similar applicability to potassium carbonate, such as being a fertilizer. (ie. potassium chloride, potassium hydroxide)

Verb

1. 1
   To treat with potassium.

Proper noun

1. 1
   A surname.