A few years ago a friend from the Catskills in upstate New York told me that when you see one of those doors on the 2nd floor of a building without any stairs leading up to it, that’s called a mother-in-law door.
Yesterday at work I told someone about “mother-in-law doors” and I decided to look up the origin on-line. The first few Google entries point to a Newfoundland origin. One explanation was that in 1949 the people of the newly-confederated Province were told by Ottawa that two doors were required in all houses, for fire safety. The Newfies being good citizens complied with the law by adding another door where needed, yet with a streak of independence they neglected to install staircases and left the doors to just open out into thin air. The mother-in-law joke naturally followed.
There is no entry in the DCHP online for mother-in-law door. Does anyone know if it’s really a Canadianism?