The Collaborative International Dictionary of English v.0.48:

Vat \Vat\ (v[a^]t), n. [A dialectic form for fat, OE. fat, AS.
   f[ae]t; akin to D. vat, OS. fat, G. fass, OHG. faz, Icel. &
   Sw. fat, Dan. fad, Lith. p[*u]das a pot, and probably to G.
   fassen to seize, to contain, OHG. fazz[=o]n, D. vatten. Cf.
   Fat a vat.]
   [1913 Webster]
   [1913 Webster]
   1. A large vessel, cistern, or tub, especially one used for
      holding liquors in an immature state, chemical
      preparations for dyeing, or for tanning, or for tanning
      leather, or the like.
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            Let him produce his vats and tubs, in opposition to
            heaps of arms and standards.          --Addison.
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   2. A measure for liquids, and also a dry measure; especially,
      a liquid measure in Belgium and Holland, corresponding to
      the hectoliter of the metric system, which contains 22.01
      imperial gallons, or 26.4 standard gallons in the United
      States.
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   Note: The old Dutch grain vat averaged 0.762 Winchester
         bushel. The old London coal vat contained 9 bushels.
         The solid-measurement vat of Amsterdam contains 40
         cubic feet; the wine vat, 241.57 imperial gallons, and
         the vat for olive oil, 225.45 imperial gallons.
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   3. (Metal.)
      (a) A wooden tub for washing ores and mineral substances
          in.
      (b) A square, hollow place on the back of a calcining
          furnace, where tin ore is laid to dry.
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   4. (R. C. Ch.) A vessel for holding holy water.
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The Collaborative International Dictionary of English v.0.48:

Vat \Vat\, v. t. [imp. & p. p. Vatted; p. pr. & vb. n.
   Vatting.]
   To put or transfer into a vat.
   [1913 Webster]

WordNet (r) 3.0 (2006):

VAT
    n 1: a tax levied on the difference between a commodity's price
         before taxes and its cost of production [syn: VAT,
         value-added tax, ad valorem tax]
    2: a large open vessel for holding or storing liquids [syn:
       tub, vat]