Thrive, making pounds in time of prosperity (5)
I believe the answer is:
bloom
'thrive' is the definition.
(thesaurus)
'pounds in time of prosperity' is the wordplay.
'pounds' becomes 'l' (L can represent the monetary pound).
'in' is an insertion indicator.
'time of prosperity' becomes 'boom' (I've seen this before).
'l' inserted inside 'boom' is 'BLOOM'.
'making' is the link.
(Other definitions for bloom that I've seen before include "Open" , "look good" , "(Come into) flower" , "Blossom, flower" , "Produce flowers" .)