Decimate. It's misused all the time. Ie the town was decimated in the bushfire. Means it was reduced by 1/10th. What they really mean was that the town was razed. Decimate does not mean destroyed.
Decimated means, according to Merriam Webster:
1- Kill, destroy, or remove a large percentage of.
2- Drastically reduce the strength or effectiveness of (something): "plant viruses that can decimate yields".
Its origins is, as you said, to reduce by 10%. Or, better yet, to punish an army by killing 1 out of 10 men, drawn by lot. However, over the centuries, it has developed new meanings. Insisting that it can only have the original meaning is a little pedantic, in my view. Or else we need to admit that forging should only be used to describe something shaped by hammering or compression (so no deal can be forged), that glass can only refer to the material and not to items made of it (drinking glass, eye glasses), that a snowflake is only something that falls from the sky and not a very special person, etc.