Ajandurah's Wand of Utter Negativity
Ajandurah's Wand of Utter Negativity was a powerful wand wielded by Marchesa, a Krullian Wizard, that was mentioned in The Colour of Magic. Possibly a relic left over form the time of soucerery. Rincewind had heard of it, was very afraid of it, and defined it as a "piece of sudden death". He also commented that if he had a wand like that, he wouldn't be afraid of anything. Therefore, the fact that Marchesa was actually afraid of Rincewind while holding the wand came as a shock. Still, she threatened to use it on Rincewind if he tried to intone the Great Spell lodged in his mind.
How it works is unknown - but it apparently its use causes the victim not simply to cease to exist, but also never to have existed. Some may consider this no different from just dying, but as well as all you life's actions never having taken place, if you never existed it would mean you never had a soul and could not go on to any of the afterlives or reincarnate as would be the usual case when people die. An extremely dangerous device, discouraged at Unseen University.