Long, but all are unalterably set (5)
I believe the answer is:
yearn
'long' is the definition.
(synonyms)
'all are unalterably set' is the wordplay.
I cannot quite see how this works, but
an anagram of 'are' is 'ear' which is within the answer.
This explanation may well be incorrect...
'but' acts as a link.
Can you help me to learn more?
(Other definitions for yearn that I've seen before include "Mark of injury" , "Have strong desire" , "lust" , "wish" , "Have a great longing" .)