To me...the most lethal weapon is the human body. Without humans, guns, bows, cannons, planes, bombs, all of them would not exist on Earth today.
The human body is the perfect example of accuracy, precision, strength and balance. It's the weapon that can think for itself. At least for the time being, till the Robot Age.
A mystical stick that, if pointed towards somebody, drives a person mentally insane, giving them the uncontrollable urge to kill their friends and family, and then end killing themselves. And yes... I am a psychopath.
this sounds an awful lot like the gun from my book... So far, I haven't mentioned it, but I have mentioned the turret version... (Oh and it is the most powerful weapon, aside from a couple which you don't even want to think about...)