Trollbane (axe)

Source
Trollbane can be looted from the reward chest after successfully doing the timed events on Zul'Aman.

Speculation
It may have a connection to Trol'kalar or the Trollbane family. In Tides of Darkness, Thoras Trollbane is described as wielding an axe. It is also highly probable that this is the original Trollbane. The original Arathor tribe were akin to barbarians (Although this may have only been in comparison to the Elves), and it is very likely that they'd use axes which are a somewhat primitive yet effective weapon.

Another possibility is that Trol'kalar, repeatedly refered to as a sword, was broken and the pieces of the blade reforged into an axe by the Horde when they took it from Trollbane's tomb to use against the jungle trolls of stranglethorn. The Horde, orcs in particular, favor the axe as their weapon of choice, and might have wanted to remake the weapon for both practical and symbolic reasons. How it ended up in the hands of the Amani, however, would be unexplained by this theory.