Missionaries working in Algonquian languages needed a word for God, and manidoo is the word they took. With the superlative attached it became Gichi-Manidoo, the great manidoo, and that compound now stands at the head of most modern accounts of Anishinaabe religion, is used in prayer, and is what an Anishinaabe person will most often offer an enquirer as the answer to who the highest being is.
What that history means for the older usage is disputed, and the dispute is genuine rather than a technicality. One position holds that a highest power was already there, that early records simply recorded it, and that the missionary usage fitted an existing idea rather than creating one. The other holds that the translation hardened something diffuse: that manidoo named a quality of power distributed across many beings, that the superlative was an available construction rather than a name in use, and that a monotheist-shaped supreme being took its present outline in the encounter. The evidence is difficult because the earliest written records are themselves missionary, so the instrument and the object are the same.
The atlas records the argument on the Anishinaabe Religion entry as a debated atom with both camps named, and does not settle it. What is not in dispute is the working vocabulary: manidoo is in daily religious use, Gichi-Manidoo is addressed, and a reader who wants to know what Anishinaabe people mean by it should ask Anishinaabe people rather than a nineteenth century dictionary.