Mississippi and Tennessee = Mississippennessee 
Western Kansas, Western Nebraska, Eastern Wyoming and Eastern Colorado–The High Plains. Eastwood even made a movie with that in its title.
Never really caught on big but there was an attempt to promote “The Inter-Mountain West” from New Mexico to Montana.
What I was taught in grade school in Oregon (way back when) was that the “Pacific Northwest” was only OR and WA. “Northwest” was all three. In the years since, although not everybody is consistent, these are by far the most common meanings.