The Collaborative International Dictionary of English v.0.48:

Mash \Mash\, v. t. [imp. & p. p. Mashed; p. pr. & vb. n.
   Mashing.] [Akin to G. meischen, maischen, to mash, mix, and
   prob. to mischen, E. mix. See 2d Mash.]
   To convert into a mash; to reduce to a soft pulpy state by
   beating or pressure; to bruise; to crush; as, to mash apples
   in a mill, or potatoes with a pestle. Specifically (Brewing),
   to convert, as malt, or malt and meal, into the mash which
   makes wort.
   [1913 Webster]

   Mashing tub, a tub for making the mash in breweries and
      distilleries; -- called also mash tun, and mash vat.
      [1913 Webster]