Witch hunter's sword is a steel sword in The Witcher 3: Wild Hunt and comes in the following forms:
Witch hunter's sword (crafted)[]
Oddly, its icon is different from all the other versions, but the sword itself looks the same.
Crafting Requirements 
Min. Required Level: Journeyman blacksmith
Witch hunter's sword (basic)[]
Dropped by witch hunters and the Prison Warden during the main quest, The Great Escape. It is also available as random loot starting at level 27 and can be purchased from the following merchants:
- All blacksmiths in Skellige
- Merchant at the Isolated Hut on Hindarsfjall
With no level restrictions, one is guaranteed to appear along with Diagram: Witch Slayer on a witch hunter's corpse by a drowner nest on the swampy coastline far west of the Orphans of Crookback Bog, further southwest from Leslav.