Shamanism is the system — the beliefs and the practices — around shamans. The ending -ism turns the person-word into the “ism”: the way of doing things, not the person. In that system, a gifted or trained person is thought to travel between the ordinary world and the spirit world, often to heal or to speak for the community. The English word is simply shaman plus -ism. It started as a way to talk about the Siberian Evenki world and then got used for similar practices elsewhere. Though actually, specialists argue about that second step. Not every traditional healer belongs under this one label, and using one Siberian word for the whole earth can flatten differences. Still, in ordinary English, shamanism is the name of that kind of spirit-work as a whole. If you need the person, say shaman.