I am not exactly sure but from my understanding, through the explanations other people give, a shaman is a sort of witch/priest/medicine man. I also think this is either a term from the continent of the Americas or perhaps somewhere in Asia.
We have witches in Europe. Having lived in North America for quite a while now, I realize the "witch" term has a negative connotation for many people. Perhaps that is why the shaman term is used, this is just a simple speculation.
A shaman is a sorcerer for me. Any term is good though: shaman, wizard, medicine man, witch, etc. I do think "medicine-man" is the closest other term, next to "shaman", I think it has to do with their healing abilities.
This is just an opinion. Thank you for the question.