Mend is a command used at shops to restore the condition of weapons and armor. Additionally, many weapons can be mended in the field by use of an oilstone or a sandstone, depending on their type.
In Game Description[]
Syntax: mend <item> give receipt <armorer/weaponsmith> Weapons and armor will degrade over time and use, gradually wearing their way towards becoming tattered and useless. However, weaponsmiths and armorers provide a service to keep your equipment in tip-top shape. Approaching one and asking them to mend one of your items will cause them to take your item, and give you a receipt in exchange. Once your item has been repaired, you can give the receipt to the weaponsmith/armorer and, for a modest price, they will return your item in improved condition. Only weaponsmiths and armorers will mend your weapons and armor. Make sure you do not give receipts to other mobs that resemble the weaponsmiths and armorers.