Gynvael Aedd is a silver sword in The Witcher 2: Assassins of Kings and The Witcher 3: Wild Hunt.
It can be bought from Falas, a merchant in chapter III at the Loc Muinne amphitheatre. The sword can also be found on a corpse in the Sewers during The Secrets of Loc Muinne. It is of elven origin, as its name means ice shard in Elder Speech, which is similar to Aedd Gynvael, the name of a city in Narok.
The Witcher 3: Wild Hunt[]
It can be obtained through the treasure hunt quest Ironsides' Treasure or as random loot.