Fair enough, I'll dial down the criticism a little, but it really did feel like you were looking for a reason that it mean 1/10th rather than using the material immediately confronted with if you googled said word. Respected dictionaries all specific state that the "1/10" meaning is historic.

I know my friends wouldn't know decimate is 1/10 and would roll my eyes if I explained its historic useage vs what everyone uses it for, but you are probably right with your last point.