All my life, I thought that "roommate" mean "someone with whom one shares a room". I had a roommate at Smith. We shared a room. Some people on campus had suitemates; they shared a hallway and a door to the main hallway. Lots of other people lived in my house on campus; they were my housemates.
Yet apparently, in American, a "roommate" is someone with whom one shares a residence, whether room, suite, apartment, flat, or house. By these standards, I had 50+ "roommates" as an undergraduate. How very confusing! How on earth do Americans distinguish room-sharing, from sharing any other scale of accomodation?