The Collaborative International Dictionary of English v.0.48:

Touchwood \Touch"wood`\, n. [Probably for tachwood; OE. tache
   tinder (of uncertain origin) + wood.]
   [1913 Webster]
   1. Wood so decayed as to serve for tinder; spunk, or punk.
      [1913 Webster]

   2. Dried fungi used as tinder; especially, the Polyporus
      igniarius.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Agaric \Ag"a*ric\ (?; 277), n. [L. agaricum, Gr. ?, said to be
   fr. Agara, a town in Sarmatia.]
   1. (Bot.) A fungus of the genus Agaricus, of many species,
      of which the common mushroom is an example.
      [1913 Webster]

   2. An old name for several species of Polyporus, corky
      fungi growing on decaying wood.
      [1913 Webster]

   Note: The "female agaric" (Polyporus officinalis) was
         renowned as a cathartic; the "male agaric" (Polyporus
         igniarius) is used for preparing touchwood, called
         punk or German tinder.
         [1913 Webster]

   Agaric mineral, a light, chalky deposit of carbonate of
      lime, sometimes called rock milk, formed in caverns or
      fissures of limestone.
      [1913 Webster]