Means to serve a summons (7)
I believe the answer is:
process
This clue is a triple definition!
'means' is the first definition.
(thesaurus)
'to serve' is the second definition.
('process' can be a synonym of 'serve')
'a summons' is the third definition.
(I know that summons can be written as process)
(Other definitions for process that I've seen before include "Series of actions with a single purpose" , "Method of production" , "Series of actions to achieve a result" , "The case" , "that's the course of action" .)