Diagram: Grandmaster Feline silver sword is a crafting diagram in the Blood and Wine expansion for The Witcher 3: Wild Hunt.
This diagram is found along with 2 others (steel sword and gauntlets) during the quest, Scavenger Hunt: Grandmaster Feline Gear, which is started after meeting and talking with Lazare Lafargue about finding grandmaster gear for 5 of the witcher schools.
With a New Game +, this diagram is replaced with the grandmaster legendary version.