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