Say order preserves island's self-interest (6)
I believe the answer is:
egoism
'self-interest' is the definition.
(synonyms)
'say order preserves island's' is the wordplay.
'say' becomes 'eg' (both can mean for example).
'order' becomes 'om' (Order of Merit).
'preserves' is an insertion indicator.
'island's' becomes 'i's' (geographical abbreviation).
'om' placed around 'is' is 'oism'.
'eg'+'oism'='EGOISM'
(Other definitions for egoism that I've seen before include "sense of superiority" , "self-centred doctrine" , "Self interest" , "Self-seeking" , "Self-centredness, vanity" .)