The sword-hilt appears to be of Westernesse-make, but the blade has been overlaid with writings in Black Speech. Among the dark writings, you can make out the name Abb.
You should take the blade to Nethraw at the Krusle Lannan to the east of Gabilshathur.
You have recovered one of the seven swords of Krusle Lannan.
Bring the Sword of Abb to Nethraw
Nethraw can be found at the Krusle Lannan, east of Gabilshathur.
You should bring the sword you found to Nethraw.
To begin this quest, you must find and kill Owen and loot The Sword of Abb from his corpse, once the sword is in inventory, click on it to start the quest.
This is one of seven quests involved in the deed:
The Seven Swords
Owen can be found at 1.8N 24.6W.