1. WHICH: is a relative pronoun and it means "what one?" or "quale?".
2. WITCH: is a noun and is a person who practices witchcraft ("strega")
3. WICH: is either an extremely rare noun meaning a bundle of thread ("un fascio di fili"). Or it can be used as a suffix "-wich" such as in sandwich ("panino").
Don't confuse these three similar words which are all pronounced the same in English!