decimāre

Decimate comes from Latin decimāre (to select by lot and kill every tenth man), from decimus (tenth), from decem (ten). In the Roman army, decimation was a punishment for mutiny, cowardice, or desertion applied to an entire unit. The soldiers were divided into groups of ten, drew lots, and the unlucky one was beaten or stoned to death by the other nine. The survivors then received barley rations instead of wheat and were forced to camp outside the defensive perimeter.

The punishment was rare because it was counterproductive — you destroyed ten percent of your own fighting force. But its rarity made it terrifying. Crassus famously decimated his legions during the war against Spartacus in 71 BCE, and the threat alone was usually sufficient to restore discipline. The logic was merciless: the randomness of the lot meant that bravery could not save you, and the requirement that your own comrades kill you destroyed unit solidarity.

English borrowed 'decimate' in the 1600s, initially preserving the precise meaning of killing one in ten. But by the 19th century, the word had drifted to mean 'to destroy a large proportion of' and eventually 'to devastate completely.' This shift infuriates purists, who argue that decimate should only mean a ten-percent reduction. The prescriptivists have lost: modern usage overwhelmingly means 'to destroy most of something.'

The battle over 'decimate' has become a proxy war in the larger conflict between descriptive and prescriptive linguistics. Prescriptivists see the loss of the Latin precision as a corruption. Descriptivists point out that language always moves toward emotional truth: a word that sounds devastating now means devastating. The Roman math was always secondary to the Roman horror.