Boneblade

Boneblade is a level 4 dagger in terms of magical enchantment and not a generic enchanted weapon. It can inflict 1d4 +4 points of damage and it has -4 THACO, a speed factor of 0 and it weighs 1 lbs. This item appears in Baldur's Gate II: Shadows of Amn and Baldur's Gate II: Enhanced Edition. It's not known where this item can be acquired.

In-game description
"Dagger +4: 'Boneblade' This seemingly simple dagger, steel blade and bone handle, is an incredibly powerful weapon. Forged by an unfortunate duergar smith centuries earlier, the handle was carved from a tooth of a black dragon and the blade was tempered in the blood of its creator. How it has made its way to you is anyone's guess."