Holiday island’s restrained by well-ordered social solidarity (9)
I believe the answer is:
tribalism
'well-ordered social solidarity' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'holiday island's restrained by' is the wordplay.
'holiday' becomes 'trim' (I can't justify this - if you can you should give a lot more credence to this answer).
'island's' becomes 'Bali's' (Indonesian island).
'restrained by' indicates putting letters inside.
'trim' going around 'balis' is 'TRIBALISM'.
Can you help me to learn more?
(Other definitions for tribalism that I've seen before include "Organisation of society on ethnic lines" , "Clannishness" , "divisive tendency" , "allegiance to group" , "Failure to transcend clan loyalty" .)