Silver Sword

Silver Sword +3 is an enchanted two-handed sword with the ability to instantly kill enemies that fail a -2 save vs. Death. This sword is availible in Baldur's Gate II: Shadows of Amnand Baldur's Gate II: Enhanced Edition. It is gained by bringing the Silver Blade, Silver Hilt and 7500 gp to Cromwell in the Athkatla Docks. You get the Silver Blade from Saemon Havarian in return for helping him get a new ship or pickpocketing him. If you have the Blade then after you return to Athkatla in Chapter 6 and go to one of the major locations in the city (Waukeen's Promenade most likely) you will run into a Githyanki named Kruin who demands that you hand over the Silver Blade. You can either give it to him or decide to fight with him and his friends. Apart from other loot he drops the Silver Hilt and if you have the gold you can visit Cromwell to have the sword made.

In-game description
"This vorpal Silver Sword radiates a dark aura when you examinate it, and the blade is so finely sharpened it could likely sever a head in a single blow."