When the Plains Indians first learned English, it was from the Army and the occasional trader or trapper who met them.  They then used the words to try to communicate to a people who might have several meanings in English and many more in Sioux or Cheyenne.  The word "medicine" in speaking or interpreting English was applied to anything sacred or powerful, mysterious or curative.  The Oregon Trail was called the Holy Road or the Medicine Road.  It was mysterious because numberless people in wagons pulled by funny looking buffalo went west but no one ever returned.  Everyone knew that when you went somewhere from home, you returned - eventually.  It would be a couple of decades before the leaders understood the meaning of the immigration and became alarmed when it disrupted life as they had know it for all the generations they could account for.