Make quiet money (4)
I believe the answer is:
dosh
'money' is the definition.
(I've seen this in other clues)
'make quiet' is the wordplay.
'make' becomes 'do' (synonyms).
'quiet' becomes 'sh' (both can be said to tell someone to be quiet).
'do'+'sh'='DOSH'
(Other definitions for dosh that I've seen before include "Money (sl.)" , "Contents of purse" , "Shod (anag.)" , "Ready" , "cash" .)