Roller coaster (3,6)
I believe the answer is:
big dipper
'roller coaster' is the definition.
(synonyms)
This is all the clue.
(Other definitions for big dipper that I've seen before include "Amusement park attraction" , "switchback" , "Familiar US stars" , "Roller coaster - The Plough (in the US)" , "Fairground ride" .)