an open automobile having a front seat and a rumble seat
"The vintage roadster we rented at the rally had only two seats, so I pushed my friend onto the rumble seat behind us."
A horse for riding or driving on the road.
"The coachman led a spirited white roadster out to the stable before dawn."
The word roadster comes from combining "road" with the suffix "-ster." It originally meant a vehicle designed specifically for driving on roads.