Decimate

I have been reading an otherwise excellent book but the author uses the word "decimate" incorrectly.

I see the same use in a number of other instances and it bugs me. From WikiPedia:

Decimation (Roman army)
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."

Procedure
A unit selected for punishment by decimation was divided into groups of ten; each group drew lots (Sortition), and the soldier on whom the lot fell was executed by his nine comrades, often by stoning or clubbing.[citation needed] 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.

So if X is decimated, 90% of X will remain while 10% of X will be destroyed. Call me a grammar grouch but...