Regrettably, "decimate" now seems to mean leaving only one out of ten alive. And it is often applied to inanimate objects. I saw a news item about a volcanic eruption decimating a city.

I think it's gotten way more general than that. It is used all the time in the news (as I mentioned above) to mean something like "destroy a substantial part of". (Not that the news should necessarily be a prime source of wordly advice!)