Sword of Undead Slaying

From LSWiki

Owned by a permanent resident of the graveyard in Corna.

   This is a finely-crafted pearlescent steel longsword.  Engraved into the
hilt is the image of a skull with a diagonal line through it.  You recognize
this as one of many blessed swords of undead slaying created years ago to
oppose the master thanaturge Necrolak and stem the tide of his undead plague. 
It is permeated by a dim pearlescent light.  You estimate its value at about
three hundred thirty gold.  
   It is in perfect condition.  
   It looks about a quarter of a dimin wide and thirteen and a half dimins
long.  It weighs about one and a tenth dekans.

   After a moment, the knowledge that the pearlescent steel longsword of
undead slaying is composed of fifty percent steel and fifty percent kedusham
drifts into your mind like a long-forgotten memory.

• Extra damage when wielded against the undead (how? why? someone more patient should get details)