Daystar

Daystar is an enchanted longsword, a +2 weapon in terms of the level of enchantment and it has +2 bonus to thaco and damage. But it has a +4 bonus against evil aligned creatures for thaco and damage and the weapon deals double damage against any undead creature. The wielder may also use this weapon once per day to cast the spell Sunray, which is a very devastating spell against the undead and also harm living creatures who are enemies. This item appears in Baldur's Gate II: Shadows of Amn. It can be found in the secret room of the Crooked Crane inn in the Athkatla City Gates area. The room is inhabitated by a lich, which makes it difficult to obtain the blade early.

In-game description
"Sunblade: Daystar Whether created specifically for use in the service of Torm or appropriated at some point in the long history of the church, Paladins of the Loyal Fury have made good use of Daystar in their battles against evil undead. Through magic or blessing it is empowered with the Sunray, a force of pure life energy so potent that it slays both living and unliving."