mansionette

noun2

1. •
   (UK) A flat that spans two or more floors, and often has its own entrance (i.e. not off a communal hallway).

   • gone to London to work and had left her mansionette flat empty. The mansionettes stood on high ground overlooking the docks. — 2014
2. •
   (US) A large and somewhat luxurious house.

   • In the smaller plans of a "Mansionette near Wimbledon Park," "Semi-detached Houses," and "The Compact House built near Blackheath," we are not favoured with any scale. — 1860