The wilderness sword 4 is a reward from completing the elite Wilderness Diary tasks given to you by the Lesser Fanatic in Edgeville, and can be retrieved from him for free if lost.
Its stats are identical to the adamant sword, which makes it a rather inefficient weapon when compared to the skills and costs required to acquire it. It should only be used for aesthetic factors, especially when you consider that the sword does not need to be equipped to benefit from its Diary bonuses, only held in the inventory. Because Desert Treasure (and consequently the Waterfall Quest) is necessary to complete the diary, it is not a feasible weapon for 1-Attack Pures.
The sword's design is based on the macuahuitl, a wooden sword with obsidian blades that was used by different civilisations in Mesoamerica, such as the Aztecs.