Source : Webster's Revised Unabridged Dictionary (1913)

Wad \Wad\, Wadd \Wadd\, n. (Min.)
      (a) An earthy oxide of manganese, or mixture of different
          oxides and water, with some oxide of iron, and often
          silica, alumina, lime, or baryta; black ocher. There
          are several varieties.
      (b) Plumbago, or black lead.