maisonette

noun

1. a small house, especially one connected to a large apartment building.
2. an apartment, usually of two floors connected by an internal staircase; duplex apartment.

noun

1. self-contained living accommodation often occupying two floors of a larger house and having its own outside entrance

n.1818, “small house,” from French maisonnette, diminutive of maison “house” (11c.), from Latin mansionem (see mansion). Meaning “a part of a building let separately” is from 1912.