automobile vs roadster

automobile

noun
  • A type of vehicle designed to move on the ground under its own stored power and intended to carry a driver, a small number of additional passengers, and a very limited amount of other load. A car or motorcar. 

adj
  • Self-moving; self-propelled. 

roadster

noun
  • An open automobile having a front seat and a rumble seat. 

  • A person who lives along the road. 

  • a sea-going vessel riding at anchor in a road or bay. 

  • A clumsy vessel that works its way from one anchorage to another by means of the tides. 

  • A bicycle, or tricycle, adapted for common roads, rather than for the racing track, usually of classic style and steel-framed construction. 

How often have the words automobile and roadster occurred in a corpus of books? (source: Google Ngram Viewer )