granny flat n. a separate apartment built on a lot already containing a home. (source: Double-Tongued Dictionary)
Further reading
In 1916, a small-town newspaper in Pennsylvania printed a fanciful item about a local gathering with a guest list that included, among others, Miss Ella Vader, Mr. Ray Zor, and other punny names. This is part of a complete episode. Transcript of...
Trivia time! Where in the United States can you visit Soda City? If you answered Columbia, South Carolina, you’re right! This nickname apparently derives from an old practice of abbreviating Columbia as Cola. The locals then referred to the town as...