The Hungering Cold

The Hungering Cold is a tanking one-handed sword and also a great offhander for rogues. Fury warriors benefit from this item as well, as its fast speed makes them generate rage significantly faster than they would have with a slow weapon such as Gressil, Dawn of Ruin.

Source
This item was a drop from Kel'Thuzad in the original Naxxramas.

Speculation
The reference to hungering and cold and similar appearance to Arthas' Frostmourne may suggest that this sword is one of the runeblades used by Ner'zhul's death knights.