mid-15c., decimacioun, "the paying of tithes, a tithing, a tax of 10% on income," from Old French decimacion and directly from Late Latin decimationem (nominative decimatio) "the taking of a tenth," noun of action from past-participle stem of Latin decimare "the removal or destruction of one-tenth," from decem "ten" (from PIE root *dekm- "ten").
As "punishment by capital execution of every tenth man, chosen by lot," from 1580s; loose or transferred sense of "destruction of a great but indefinite number, severe loss" is attested by 1680s.
