To destroy or kill a large part of (a group).
To inflict great destruction or damage on.
To reduce markedly in amount.
To select by lot and kill one in every ten of.
Decimate was originally a military term and referred to discipline within a Roman legion. It was a serious punishment in which ten percent of the legion was executed in punishment for the failure of the legion. It has been used in a martial context generally in reference to casualties inflicted upon an enemy force. To decimate an enemy force was to kill or incapacitate ten per cent of the force. The term is often confused with devastate.
Within the realm of knife fighting, I have not seen the term used. However, I can see it being applicable. How much do your arms weigh? Are they 10% of your body weight or more? The vast majority of Aikidoka that I have trained with, sparred with, or observed keep their arms relatively immobile, pushed out like antennae, when they are in their "ready" stance. Filipino martial arts practitioners do not do this. The arms are mostly in motion, because they are targets (one of the primary targets during the initial entry against the opponent) for the blade. I do not associate or train with Mr. Harden, but I have been told that he likes khukuris. I have a few of these knives, though, for big knives I generally prefer a fighting bowie. In recent tests of a pair of Cold Steel Bowies (a San Mai III Laredo Bowie and San Mai III TrailMaster) that I conducted for a magazine article, I performed multiple cuts per second with these big blades, severing huge pieces off of my cutting media. WIth a bit of training, this is not difficult to do at all, even while conducting footwork and using the off hand to deflect, distract, hit, parry, bridge, or trap. There is no warning. There is no windup. There is no telltale twitch of the shoulder muscle so prevalent when most people attempt to initiate a cut. There is simply a snap down and a snap up, and, in the blink of an eye, two arms are laying on the floor severed at or near the elbow. If the arms do not weigh ten percent of the total weight of your body, I am sure that other pieces can pretty much be severed at will until the desired weight is reached. Yes you can move and defend, but, against someone skilled in the use of the blade, the smart money is going to be betting on twitchy little bits of you laying on the floor rather than a spectacular disarm and throw of the "disgusting blade wielding thug."