Class system (5)
I believe the answer is:
order
This clue is a double definition.
'class' is the first definition.
(I've seen this in another clue)
'system' is the second definition.
(I've seen this before)
(Other definitions for order that I've seen before include "Command, mandate" , "goods supplied" , "Direction; class; arrange" , "Type of column" , "Command or requisition." .)