A rich man takes the plunge (5)
I believe the answer is:
dives
I believe this is a double definition.
'a rich man' is the first definition.
(rich man in the Bible)
'takes the plunge' is the second definition.
(I've seen this in another clue)
(Other definitions for dives that I've seen before include "Disreputable bars" , "Gets into water" , "Someone loaded" , "Seedy clubs" , "sort of nightclubs?" .)