The Collaborative International Dictionary of English v.0.48:

Leach \Leach\, n. [Written also letch.] [Cf. As. le['a]h lye,
   G. lauge. See Lye.]
   1. A quantity of wood ashes, through which water passes, and
      thus imbibes the alkali.
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   2. A tub or vat for leaching ashes, bark, etc.
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   Leach tub, a wooden tub in which ashes are leached.
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