We all have pet peeves. Writers tend to have a lot of very nitpicky, word-related pet peeves - hobbyhorses, in Laurence Sterne's phrasing - and the word decimate is one of mine. People use decimate to mean "wiped out" or "totally destroyed" all the time. The usage is common enough that it's become correct, according to most dictionaries, which I resent. (Did you know dictionary entries are ordered by age? The oldest use of the word comes first, the newest last.)
The thing is, English already has plenty of words that mean "wipe out" or "totally destroy": devastate, annihilate, demolish, obliterate, wreck. Why take a word with a unique meaning and history and lump it in with a bunch of interchangeable synonyms?
I'll refer to wikipedia for further explanation:
Decimation (Latin: decimatio; decem = "ten") was a form of military discipline used by officers in the Roman Army to punish mutinous or cowardly soldiers. The word decimation is derived from Latin meaning "removal of a tenth."
A unit selected for punishment by decimation was divided into groups of ten; each group drew lots, and the soldier on whom the lot fell was executed by his nine comrades, often by stoning or clubbing. The remaining soldiers were given rations of barley instead of wheat and forced to sleep outside the Roman encampment.
Because the punishment fell by lot, all soldiers in the group were eligible for execution, regardless of the individual degree of fault, or rank and distinction.
The leadership was usually executed independently of the 1 in 10 deaths of the rank and file
And the wikipedia article links to a more complete explanation here, which sources the term in a couple of Latin histories.
The really great thing about a word like decimate is it allows us to be specific. It derives from a practice that was literally horrific - intended to inspire horror - and it allows us to describe small losses that have a huge impact. If one-tenth of a city is destroyed by an earthquake or flood, it's been decimated. If you have ten family members and one of them dies, your family has been decimated by loss. If one house on a street with ten houses burns down, that's decimation.
Using the word properly allows us to give those losses the weight they deserve. It reminds us that life isn't a numbers game. Little ten-percent horrors can derail us, change our lives, turn everything topsy turvy.
So. In short. Decimate. To reduce by one-tenth. Go forth and use it properly.