witch != shaman. Both are complicated concepts with culturally-specific meanings. Overlap is limited, and they're certainly not synonyms.
La Tiene celts were ~animist in 200BC, so shaman seemed a reasonable modern word here. I suppose "druid" would also be OK, but I don't think scholarship has much to say about continental druidism, and what the consensus is generally is "they were probably called that and beyond that we really have no idea". (because we've long since lost anything close to a primary source, among other things)
i can imagine though, that a shaman in old times Europe, could have been identified by the church as a witch. (as confused we are about the definitions today, they probably were even more so back then.)