threshing or thrashing, separation of grain from the stalk on which it grows and from the chaff or pod that covers it. The first known method was by striking the reaped ears of grain with a flail. In another early method horses or oxen trod out the grain from stalks spread on a threshing floor. In both cases the straw was raked away and then the mixture of grain and chaff was winnowed, i.e., tossed into or poured through a current of air so that the light chaff was blown away from the heavier grain. In 1784 a Scotsman, Andrew Meikle, devised a threshing machine. Sheaves of grain were fed into a revolving cylinder armed with wooden beaters. Another toothed drum raked away the loose straw and pushed the remaining chaff and grain through a sieve onto a series of rollers that further separated the chaff from the grain in preparation for winnowing. The principle of Meikle's machine has been retained in all threshing machines up to and including the modern self-propelled combines.
See M. Partridge, Farm Tools through the Ages (1973).
thresh / [unvoicedth]resh/ • v. [tr.] 1. separate grain from (a plant), typically with a flail or by the action of a revolving mechanism: machinery that can reap and thresh corn in the same process | [as n.] (threshing) farm workers started the afternoon's threshing. 2. variant spelling of thrash (in the sense of violent movement).
Hence thresher (-ER1) person or machine that threshes XIV; shark so named from the upper division of its tail with which it lashes an enemy XVII.