The Collaborative International Dictionary of English v.0.48:

Thrashing \Thrash"ing\,
   a. & n. from Thrash, v.
   [1913 Webster]

   Thrashing floor, Threshing-floor, or Threshing floor, a
      floor or area on which grain is beaten out.

   Thrashing machine, a machine for separating grain from the
      straw.
      [1913 Webster]

WordNet (r) 3.0 (2006):

threshing floor
    n 1: a floor or ground area for threshing or treading out grain