Source : Webster's Revised Unabridged Dictionary (1913)

Thresh \Thresh\, v. t. & i. [imp. & p. p. {Threshed}; p. pr. &
   vb. n. {Threshing}.]
   Same as {Thrash}.

         He would thresh, and thereto dike and delve. --Chaucer.

Source : WordNet®

threshing
     n : the separation of grain or seeds from the husks and straw;
         "they used to do the threshing by hand but now there are
         machines to do it"