Windshear

Windshear is a unique Scimitar found in. Although its appearance is identical to the Scimitar, the enchantment is one of a kind and cannot be disenchanted.

Acquisition
This sword can be obtained during the Dark Brotherhood quest Hail Sithis!, on a ship called The Katariah; this ship can only be accessed during or after the quest.

Proceed onto the main deck of the boat. Follow the stairs that lead to the bow (the front of the ship). Here a long wooden beam protruding from the bow (Bowsprit) is located. Carefully walk up the beam to the top where Windshear will be visible, wedged into the wood.

Enchantment
The enchantment of Windshear is described as "Bash attacks made with this weapon have a chance of knocking enemies down". In combat, this translates to block-bashing having a 30% chance to paralyze an enemy for 0.1 seconds. Block-bashing is only possible when the off-hand is unarmed.

Additionally, Windshear inflicts a powerful stagger effect when used regularly in combat. This effect is a more powerful than the aforementioned enchantment; rather than chance, every attack staggers any enemy 100% of the time.

Usefulness

 * The stagger effect of Windshear is useful in defeating almost any enemy, as repeated strikes completely inhibit them from attacking or retreating.
 * This is one of several special 'Named' weapons in the game, each of which is discovered along one guild's Questline. They are: Chillrend, Ysgramors Axe, and the Staff of Magnus, respectfully.

Smithing
Windshear can be upgraded with a Steel Ingot at a grindstone. The Steel Smithing perk doubles the improvement.

Bugs

 * The weapon may spawn under the forward mast, hovering in mid air making the weapon difficult if not impossible to acquire normally. One can, however, simply shoot this down using an arrow or a destruction spell, and retrieve it from the water below.
 * This weapon also seems to get "stuck" in your hand when unequipped. This can be fixed by unequipping and reequipping any gloves/gauntlets.
 * On rare occasions the weapon may spawn normally, but then fall into the water below.