*double-decker*

n. 1. (Naut.) 1. A man-of-war having two gun decks. [ 1913 Webster ]

2. (a) A tenement house having two families on each floor. [ Local, U. S. ] (b) A biplane aëroplane or kite. [ Colloq. ] [ Webster 1913 Suppl. ]

3. anything having two decks or levels, as a bus with two levels for passengers. In older vehicles, less often today, the upper deck was open, as on street cars. [ Colloq. ] [ PJC ]