The Collaborative International Dictionary of English v.0.48:

Leach \Leach\, v. t. [imp. & p. p. Leached; p. pr. & vb. n.
   Leaching.] [Written also leech and letch.]
   1. To remove the soluble constituents from by subjecting to
      the action of percolating water or other liquid; as, to
      leach ashes or coffee.
      [1913 Webster]

   2. To dissolve out; -- often used with out; as, to leach out
      alkali from ashes.
      [1913 Webster]

WordNet (r) 3.0 (2006):

leaching
    n 1: the process of leaching [syn: leach, leaching]