Yeah and wiedźma has the same root as wiedzieć and to know in proto indo-european.
He's a man of knowledge. About killing things out of this world.
Canonically witchers world coexists in our own multiverse and was similiar to our own reality, but thanks to some bonduary bluring between cosmic realms got tainted hundreds years ago by otherwordly magic and monsters.
So the whole witcher, wiedźmin name just indicates knowledge, an is likely a name given to them by common people instead of being an endonym.