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this only means to reduce by a tenth.
Maybe if we're going to spend some time in pendants corner you should look at third meaning in the mirriam Websters definitions. Whilst it's true the origin is in the Latin for reduce by a tenth, meaning of words evolve.
From your same link
Decimate strayed from its "tenth" meaning and nowadays refers to the act of destroying or hurting something in great numbers.
this only means to reduce by a tenth.
I'd opt for eradicating all of them and Reform / BNP voters... but I think eradication is still politically and ethically distasteful, oh well.