Actually, decimated means killing one out of ten. Comes from the Roman practice of doing just that with soldiers if they failed in battle and needed extra motivation.
Decimation in the Roman legions was usually reserved for those legions that mutinied. The soldiers would be separated into their groups of ten, each man having a number from 1 to 10. By lot, a number from 1 to 10 would be called out and every man with that number in each group of 10 would be killed. But those not called would still not be entirely spared. It was the job of the other nine to beat the 10th man to death. Since the groups of 10, called decades, were similar to modern squads, the nine would be beating to death one of their comrades and friend.
You have inverted it.
Decimate literally means killing 9 out of 10 or cutting the opposing force down to 1/10 of the size.
But in general it is a euphamism any route but especially any route where the force is destruyed to ranks level and requires a total rebuild.
Sorry you are right on the original meaning.
The euphamistic use still stands though...
You're the first person I've ever seen who got this right. The Latin derivation is obvious, but most people misuse the word, often used instead to mean total destruction.
Decimation - Perhaps the most gruesome punishment of all known to the Roman army was that of decimation. It generally was applied to entire cohorts and meant that every tenth man, randomly chosen by a draw of lots, was killed by being clubbed or stoned to death by his own comrades. This form of punishment of the troops was however extremely rare.