The word, is often used in combat, or when someone gets outwitted, destroyed by someone really by a large margin. Around 1663, the word decimate first appeared in that year and was used by the Roman Soldiers. The meaning wasn’t exactly the same, these days it means someone getting destroyed by a person or something similar to that. In the Roman Days it refereed to a disciplinary practice done by the Roman Army. Soldiers convicted of cowardice or mutiny regrouped in units of 10 and lots were drawn, the loser was decimated (clubbed, stoned to death) by the other nine. Morale increased in the Roman Army after a decimation, significantly.
And the other nine were not so easily let off either, they would be forced to sleep outside instead of the army pavilions and eat a very small portion instead of the other soldiers.
Although this method discouraged cowards, pushed discipline and resolve. It wasn’t very popular in the army because it reduced numbers and strength.