"Wiedzma" isn't like "wiedzmin" at all (In Polish)! - in meaing. it's two different things. I've never read or heard the world "wiedzmin" before Sapkowski's books. Moreover, "wiedzma" = "witch", in Polish is associated with female, 1. old lady, doing some dark magic with herbs and spells, mostly bad or 2. old lady using herbs to heal ppl (it's true image from history, not the false one). "Wiedzmin" is a male who uses herbs, potions and magic BUT meant to kill monsters and is a
mutated human ("wiedzma" is rather to create monsters
). I think Sapkowski invented that because we have no "wiedzma" males, it's always magician / sorcerer (mag / czarodziej) in Polish culture. In Wikipedia we have no encounter of "wiedzmin" other than connceted with Sapkowski's fiction. However, we cannot argue that the world "wiedzmin" origins from "wiedzma" but inflectionally. The best thing is to ask Sapkowski
(I'm Polish)