Keening is a dagger and Dwemer artifact.
Beneath Red Mountain, Dwemer miners discovered a great magical stone. By diverse methods, Lord Kagrenac, High Priest and Magecrafter of the ancient Dwemer, determined that this magical stone was the heart of the god Lorkhan, cast here in the Dawn Era as punishment for his mischief in creating the mortal world. Determined to use its divine powers to create a new god for the exclusive benefit of the Dwemer, Kagrenac forged three great enchanted artifacts, which are called Kagrenac's Tools. Wraithguard is an enchanted gauntlet to protect its wearer from destruction when tapping the heart's power. Sunder is an enchanted hammer to strike the heart and produce the exact volume and quality of power desired. Keening is an enchanted blade that is used to flay and focus the power that rises from the heart.
One account state Indoril Nerevar used this dagger to slay King Wulfharth at the Battle of Red Mountain and cut out the Heart of Lorkhan from his body. Following Wulfharth's defeat, all three artifacts came into the possession of the Almsivi following the Battle of Red Mountain. The Tribunal wrested Kagrenac's Tools and the Heart of Lorkhan from Voryn Dagoth and used them to give themselves divine powers. Unbeknownst to them, Voryn Dagoth did not die from their conflict but had secretly connected himself to the Heart long ago, turning into Dagoth Ur and becoming a divine being himself.
Sunder, along with Keening, was subsequently lost during an annual pilgrimage to the Heart some time in the Third Era.