au pair unit
n.— «In Colleyville, owners can buy a small, adjacent room, often called a “mother-in-law unit” or “au pair unit.” Some town houses in Bedford and North Richland Hills have front porches.» —“Some accept town houses, others not so much” by Sarah Bahari Telegram-Star (Dallas, Texas) July 8, 2006. (source: Double-Tongued Dictionary)