Operate as a party (8)
I believe the answer is:
function
This clue is a double definition.
'operate' is the first definition.
(I know that operate can be written as function)
'a party' is the second definition.
(thesaurus)
'as' acts as a link.
(Other definitions for function that I've seen before include "social gathering" , "An official ceremony" , "Role, duty" , "Formal event; mathematic expression" , "Special purpose or social affair" .)