Re: @nanchatte the P.G.N.

If you thought that was pedantic:

The reason that "decimate" gets confused with "destroy" is that poorer quality dictionaries are loose with their synonyms - they just run a thesaurus scan and pick a few words. Now, "decimate" is perfectly legitimate as a thesaurus related word with "destroy" but you won't find a reputable dictionary giving it as a synonym.

"Destroy a significant proportion of" is the widest common modern definition.