William's parliamentary business (5)
I believe the answer is:
bills
'william's parliamentary business' is the definition.
I can't judge whether this defines the answer.
'william's parliamentary business' is the wordplay.
'william' becomes 'bill'.
'parliamentary business' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'bill'+'s'='BILLS'
Can you help me to learn more?
(Other definitions for bills that I've seen before include "Draft laws" , "Invoices" , "Beaks" .)