Decimate has been getting improper usage for a long time, as it is not really that impressive to destroy 1/10 of an opposing military force in a given battle either, yet the word is customarily used as if one had wiped out at least 75% of them, in which case "devastate" would certainly make more sense...or "annihilate", in really extreme cases.

For instance, the Sioux did far more than merely "decimate" Custer's unit at Little Big Horn. I believe they more than decimated Reno's section, and they annihilated Custer's.

I believe decimate derives from a Roman practice of punishing a legion by executing every tenth man. Can anyone confirm that?

- LH