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v. Present participle of winnow.

n. The act of separating chaff from grain.

n. The act of one who, or that which, winnows.

n. the act of separating grain from chaff

"The traditional method of threshing by treading out of the grain with bullocks, followed by winnowing, is now inadequate for threshing the increased volume of wheat before the onset of the monsoon rains."

separation   

winnow