The definition "destroy a large number of" has been around for centuries. You're contradicting long established usage, while pretending to appeal to it.
I am not contradicting it. From their context it was not possible to tell if they meant the deaths of 1 in 10, a number similar to that, about half of all people, 9 in 10, 99 in 100 etc. I gave the proportions as remembered from the book as that gives a far clearer picture.
Here's the dictionary definition of decimate. The primary definition is "destroy a large number of". This isn't recent - I looked it up in the full OED and it's been around for centuries.
