a transparent dome, usually made of plastic or bulletproof glass, that serves as the roof or part of the roof of an automotive vehicle. · a vehicle having such a dome: The old van was converted into a bubbletop. Found on https://www.infoplease.com/dictionary/bubbletop
1) Dome 
a transparent dome, usually made of plastic or bulletproof glass, that serves as the roof or part of the roof of an automotive vehicle. · a vehicle having such a dome: The old van was converted into a bubbletop.