Learn how to say Rollercoaster correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word roller coaster:
a fairground attraction that consists of a light railway track which has many tight turns and steep slopes on which people ride in small, fast open carriages:
a roller-coaster ride
something characterized by wild and unpredictable changes:
a terrific roller coaster of a book
(roller-coaster, also roller-coast) [no object] move, change, or occur in a dramatically changeable manner:
the twentieth century fades behind us and history roller-coasters on