Period of economic growth (4)
I believe the answer is:
boom
'period of economic growth' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for boom that I've seen before include "Period of prosperity or sonic sound" , "Period of prosperity - explosive sound - sailing boat's spar" , "Resonant sound < of TV equipment" , "Harbour barrier" , "Resonant sound, like artillery" .)