big dipper vs roller coaster

big dipper and roller coaster both are nouns.

Word	Noun	Adjective	Verb	Adverb
big dipper	Yes	No	No	No
roller coaster	Yes	No	No	No

As nouns, big dipper and roller coaster are synonyms defined as:

big dipper and roller coaster: elevated railway in an amusement park (usually with sharp curves and steep inclines)

Other synonyms of big dipper include chute-the-chute.

big dipper (noun)	roller coaster (noun)
elevated railway in an amusement park (usually with sharp curves and steep inclines)	elevated railway in an amusement park (usually with sharp curves and steep inclines)
	anything characterized by abrupt and extreme changes (especially up and down)