Barrier for prosperity (4)
I believe the answer is:
boom
I believe this is a double definition.
'barrier' is the first definition.
(I've seen this before)
'prosperity' is the second definition.
(boom is a kind of prosperity)
'for' acts as a link.
(Other definitions for boom that I've seen before include "become suddenly prosperous" , "Loud noise - business increase" , "Pole for overhead microphone - deep sound" , "Deep hollow sound" , "pole attached to sail" .)