From the Classics: Glammad's Halberd

At Svia Skerries they fought a berserker called Glammad. He had one excellent weapon, a halberd, which could pick out any opponent as soon as the bearer knew his name.

Egil and Asmund, (Anon., 14th century AD)

Glammad's Halberd is a magical weapon that gains in martial prowess by knowing its enemy's name. The wielder must speak the name of the enemy he wishes to attack. The halberd will then gain a +3 bonus to hit and damage rolls against that enemy. Only unique, given names can be used in this way, so the halberd's power is useless against most animals.

Glammad's Halberd can also be introduced to the name of the opponent's weapon, if such a name exists. This grants the wielder a +3 defense bonus against the weapon's attacks, as the halberd moves with uncanny swiftness to block the enemy's blows.