The Collaborative International Dictionary of English v.0.48:

Pung \Pung\, n. [Etymol. uncertain.]
   A kind of plain sleigh drawn by one horse; originally, a rude
   oblong box on runners. [U.S.]
   [1913 Webster]

         Sledges or pungs, coarsely framed of split saplings,
         and surmounted with a large crockery crate. -- Judd.
   [1913 Webster]

         They did not take out the pungs to-day.  -- E. E. Hale.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pung
    n 1: a one-horse sleigh consisting of a box on runners