Weaponsmith is the skill associated with the weaponsmithing labor. Weaponsmiths make metal weapons (including crossbows), trap components, picks and bolts at a metalsmith's forge. The skill level of the weaponsmith determines the quality of the produced weapons, as well as the speed of their production. Weaponsmiths also do well in the other smithing tasks, due to the attributes needed to perform these.
Standard materials that a weaponsmith can use for most weapons are adamantine, steel, iron, silver, bronze/bismuth bronze, copper, and divine metals. (See this chart for specific comparisons and recommendations.) Exceptions include obsidian short swords (in a Craftsdwarf's workshop) and unpredictable items created during a strange mood.
Due to the necessity of weaponry in most forts and the high added value of weapons (especially quality ones) compared to their base material, a high-skill weaponsmith is a precious dwarf indeed. Honestly, you wouldn't let them go in the caverns and be eaten by some random giant cave spider, now would you?
If only he knew how many goblin heads would be sliced with that thing.Art by vertibirdo