The Collaborative International Dictionary of English v.0.48:

Thrash \Thrash\, Thresh \Thresh\, v. t. [imp. & p. p.
   Thrashed; p. pr. & vb. n. Thrashing.] [OE.
   [thorn]reschen, [thorn]reshen, to beat, AS. [thorn]erscan,
   [thorn]rescan; akin to D. dorschen, OD. derschen, G.
   dreschen, OHG. dreskan, Icel. [thorn]reskja, Sw. tr["o]ska,
   Dan. t[ae]rske, Goth. [thorn]riskan, Lith. traszketi to
   rattle, Russ. treskate to burst, crackle, tresk' a crash,
   OSlav. troska a stroke of lighting. Cf. Thresh.]
   1. To beat out grain from, as straw or husks; to beat the
      straw or husk of (grain) with a flail; to beat off, as the
      kernels of grain; as, to thrash wheat, rye, or oats; to
      thrash over the old straw.
      [1913 Webster]

            The wheat was reaped, thrashed, and winnowed by
            machines.                             --H. Spencer.
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   2. To beat soundly, as with a stick or whip; to drub.
      [1913 Webster] Thrash