Shaw: derived from the Medieval Latin word "decimatus" which related to tithing, or taking a tenth, nothing to do with punishment or killing.

Wikipedia: the word decimation is derived from Latin meaning "removal of a tenth".[1] The procedure was a pragmatic attempt to balance the need to punish serious offences with the realities of managing a large group of offenders.[2]

The American Heritage Dictionary of the English Language: Fourth Edition. 2000". Dictionary.reference.com. Retrieved 2014-03-22.:decimate: to select by lot and kill every tenth person of.