To destroy or kill a large percentage of something, or originally in ancient Rome, to punish soldiers by executing one out of every ten.
From Latin 'decimare,' from 'decimus' (tenth). Roman generals would execute one-tenth of a mutinous legion as punishment. The meaning evolved from this specific practice to mean 'destroy greatly' or 'severely reduce.'
The original Roman meaning was literally 'kill one of every ten soldiers'—which actually sounds lenient compared to other military punishments—but the brutal practice was so shocking that the word came to mean 'devastate utterly,' showing how a specific historical horror can reshape language forever.
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