Means to cut by 10.................
...percent.
It was a punishment meted out to Roman troops where one out of every ten men in a unit, say ten men out of a Century (or 400 out of forty centuries, or a full Legion), was selected at random and executed. For mutiny, disobeying orders, cowardice, etc. The French army in WWI followed a similar policy against units that refused orders to leave their trenches in suicidal attacks against German barbed wire and machine guns. It reduced the unit’s strength by ten percent, but presumably the remaining ninety percent would have gotten the message. Now it has no specific meaning except for some kind of horrendous slaughter.