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c.1600, in reference to the practice of punishing mutinous military units by capital execution of one in every 10, by lot; from Latin decimatus, past participle of decimare (see decimation). Killing one in ten, chosen by lots, from a rebellious city or a mutinous army was a common punishment in classical times. The word has been used (incorrectly, to the irritation of pedants) since 1660s for "destroy a large portion of." Related: Decimated; decimating.