This is a curious word and does not mean today what it meant to the Ancient Romans who coined the term. Merriam-Webster defines decimate as:
DECIMATE; transitive verb
1: to select by lot and kill every tenth man of
2: to exact a tax of 10 percent from
3a : to reduce drastically especially in number
b : to cause great destruction or harm to
It is 3a and b that is more commonly used today however, it is definition one where the word came from. Specifically the Roman military practice of decimation in which mutinous or cowardly units were sentenced to be decimated. This was never a common punishment, most extreme punishments are only effective if they are both extreme and rare. There are a few instances in recorded sources of a unit being decimated one of which is the Legio III Augusta which was decimated in A.D. 18 after allowing one of its subunits to be annihilated in battle.