two-seater vs runabout

two-seater and runabout both are nouns.

Word	Noun	Adjective	Verb	Adverb
two-seater	Yes	No	No	No
runabout	Yes	No	No	No

As nouns, two-seater and runabout are synonyms defined as:

two-seater and runabout: an open automobile having a front seat and a rumble seat

Other synonyms of two-seater include roadster.

two-seater (noun)	runabout (noun)
an open automobile having a front seat and a rumble seat	an open automobile having a front seat and a rumble seat