Rich member overcome by booze (5)
I believe the answer is:
ample
'rich' is the definition.
('ample' can be a synonym of 'rich')
'member overcome by booze' is the wordplay.
'member' becomes 'mp'.
'overcome by' indicates putting letters inside.
'booze' becomes 'ale' (I've seen this before).
'mp' inserted into 'ale' is 'AMPLE'.
(Other definitions for ample that I've seen before include "Copious - abundant" , "Plentiful; large" , "Easily sufficient" , "Plenty, more than enough" , "Big" .)