1590–1600; < Latin decimātus, past participle of decimāre “to punish every tenth man chosen by lot,” verbal derivative of decimus “tenth,” derivative of decem ten; see -ate¹

The earliest English sense of decimate is “to select by lot and execute every tenth soldier of (a unit).” The extended sense “destroy a great number or proportion of” developed in the 19th century: Cholera decimated the urban population. Because the etymological sense of one-tenth remains to some extent, decimate is not ordinarily used with exact fractions or percentages: Drought has destroyed (not decimated ) nearly 80 percent of the cattle.