The Collaborative International Dictionary of English v.0.48:

Shack \Shack\, n. [Cf. Scot. shag refuse of barley or oats.]
   1. The grain left after harvest or gleaning; also, nuts which
      have fallen to the ground. [Prov. Eng.]
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   2. Liberty of winter pasturage. [Prov. Eng.]
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   3. A shiftless fellow; a low, itinerant beggar; a vagabond; a
      tramp. [Prov. Eng. & Colloq. U.S.] --Forby.
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            All the poor old shacks about the town found a
            friend in Deacon Marble.              --H. W.
                                                  Beecher.
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            These miserable shacks are so low that their
            occupants cannot stand erect.         --D. C.
                                                  Worcester.
      [Webster 1913 Suppl.]

   Common of shack (Eng.Law), the right of persons occupying
      lands lying together in the same common field to turn out
      their cattle to range in it after harvest. --Cowell.
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