roadster vs runabout

roadster and runabout both are nouns.

Word	Noun	Adjective	Verb	Adverb
roadster	Yes	No	No	No
runabout	Yes	No	No	No

As nouns, roadster and runabout are synonyms defined as:

roadster and runabout: an open automobile having a front seat and a rumble seat

Other synonyms of roadster include two-seater.

roadster (noun)	runabout (noun)
a small lightweight carriage; drawn by a single horse	an open automobile having a front seat and a rumble seat
an open automobile having a front seat and a rumble seat