The Collaborative International Dictionary of English v.0.48:

Tun \Tun\ (t[u^]n), n. [AS. tunne. See Ton a weight.]
   1. A large cask; an oblong vessel bulging in the middle, like
      a pipe or puncheon, and girt with hoops; a wine cask.
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   2. (Brewing) A fermenting vat.
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   3. A certain measure for liquids, as for wine, equal to two
      pipes, four hogsheads, or 252 gallons. In different
      countries, the tun differs in quantity.
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   4. (Com.) A weight of 2,240 pounds. See Ton. [R.]
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   5. An indefinite large quantity. --Shak.
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            A tun of man in thy large bulk is writ. --Dryden.
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   6. A drunkard; -- so called humorously, or in contempt.
                                                  --Dryden.
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   7. (Zool.) Any shell belonging to Dolium and allied genera;
      -- called also tun-shell.
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