Nine-days wonder (5,2,3,3)
I believe the answer is:
flash in the pan
'nine-days wonder' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for flash in the pan that I've seen before include "First and only success" , "Nine-days wonder" , "Nine days' wonder" , "Brief success - flambe moment?" , "Failure, after initial promise" .)