Compulsory arrangement? (5)
I believe the answer is:
order
'arrangement?' is the definition.
(I know that order is a type of association)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for order that I've seen before include "rule of law" , "Tell - regulate" , "demand" , "Tidy state - that's a command" , "Ruling" .)