Now Google is your friend.

Well, sorta. It doesn't give a really detailed description. I'll have one up in a bit, though.

"They are tailored weapons." Naud replied. "Blades of sentient metal, crafted by the kinebrach metallurgists, a technique now utterly forbidden. We call them anathames. When such a blade is selected for use against a specific target, it becomes that target's nemesis, utterly inimical to the person or being chosen."

~D