One in 10
The word decimate comes to us courtesy of the inspired old Roman custom of punishing a mutiny by choosing by lot and executing one in every 10 men in a legion. Same root as decimal.
I doubt that even a die-hard purist would seriously insist on the English word’s retaining a literal etymological sense of one in 10. But how should we understand it in English? Using it in what one can argue is the most legitimate sense — to suffer a substantial damage — risks misunderstanding by the multitude of readers who have come to think of it as meaning to suffer an overwhelming loss.
The Shorter Oxford English Dictionary thinks that the looser usage rises from a misunderstanding that the word means to execute nine of 10. And in a nation that appears to have more citizens who can reach Old Church Slavonic than can calculate a percentage accurately, that theory carries weight.
I suspect that considerable responsibility for the looser meaning lies with sportswriters, who are addicted to using the language of warfare to describe grown men playing children’s games:
Dons decimate UCD bullpen
Celtics decimate Raptors
It took years for fans to forgive baseball for its apparent greed that resulted in the cancellation of the World Series, a reaction that cost the sport millions of dollars in revenue and threatened to decimate the sport.
That last example shows how far we have gone to turn a word that means the loss of a percentage of a countable total into a word that just vaguely means to damage seriously or cripple. And if sportswriters bear responsibility, they do not bear it alone:
Frequent hurricanes decimate sea turtle beaches
Global warming to decimate China’s harvests
Former Sen. Thompson’s entry could decimate second tier of ’08 hopefuls
So the precise writer is left in a fix. To use the word in the narrow sense may be misunderstood. To use it in the broad sense is distasteful. If I were you, I would avoid it altogether, unless it is possible to use it in a specific context, such as with percentages, to show exactly what you mean. Leave the sloppiness and hyperbole to the people whose taste runs to that sort of thing.