When you finish a Long Rest, you can etch a magical rune on a Masterwork weapon. When you etch a rune, choose one of the following creature types: Aberrations, Celestials, Dragons, Elementals, Fey, Fiends, Giants, or Undead. If a creature of that type takes damage from the weapon, the creature takes an extra 1d6 Force damage.
You can inscribe runes on a total number of weapons up to your Masterwork Bonus (minimum of 1). When you etch a new rune, you can remove another one.
A weapon that deals extra damage to Dragons is called a "Dragonsbane" weapon, one that deals extra damage to Giants is called a "Giantsbane," and so on.