buggy vs roadster

buggy and roadster both are nouns.

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

As nouns, buggy and roadster are synonyms defined as:

buggy and roadster: a small lightweight carriage; drawn by a single horse

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

buggy (adjective)	roadster (adjective)
infested with bugs
informal or slang terms for mentally irregular