Real Dictionary

thresh
When a cereal such as corn, wheat, or rice is threshed, it is beaten in order to separate the grains from the rest of the plant.

thresh in American English
to beat out (grain) from its husk, as with a flail
to thresh grain
intransitive verb: to thresh wheat, grain, etc.
transitive verb: to separate the grain or seeds from (a cereal plant or the like) by some mechanical means, as by beating with a flail or by the action of a threshing machine

thresh in British English
noun: the act of threshing
verb: to beat or rub stalks of ripe corn or a similar crop either with a hand implement or a machine to separate the grain from the husks and straw