Loud noise – period of prosperity (4)
I believe the answer is:
boom
I believe this is a double definition.
'loud noise' is the first definition.
(I've seen this in another clue)
'period of prosperity' is the second definition.
(I've seen this before)
(Other definitions for boom that I've seen before include "Pole on film set" , "Spar - loud noise" , "It may protect harbour" , "Deep hollow sound" , "Deep sound; spar" .)