My question concerns using names in fiction that happen to be the same as copyrighted or trademarked names. I've developed a large fictional world for my writing, with hundreds of names of people, societies, countries, groups, religions, gods, etc. How worried should I be that one of these names happens to be the same name used in another novel, game, or movie? As one example: I call the people who do witchcraft in my world "witchers." I have just learned that there is a book series and now a videogame called "The Witcher" (which is trademarked). I can find many pages describing restrictions on using copyrighted or trademarked names and images when doing fan art or fan fiction, or on using names like Burger King and Reebok when your characters use those products. But I can't tell how these laws apply to what I'm doing – using the same name, but a distinctly different idea.
I have no idea how many other names I use in my stories are also affected; if I do have to look up each one of them, what specifically should I be looking for?