Duck — plump and very rich (7)
I believe the answer is:
orotund
'very rich' is the definition.
(as in a rich and orotund voice)
'duck plump' is the wordplay.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'plump' becomes 'rotund' (I've seen this before).
'o'+'rotund'='OROTUND'
'and' is the link.
(Other definitions for orotund that I've seen before include "booming" , "Full, clear and musical" , "Of speech, pompous and imposing" , "Bombastic" , "Sonorous; pompous" .)