See scales’ arrangement is eternal (9)
I believe the answer is:
ceaseless
'is eternal' is the definition.
(thesaurus)
'see scales' arrangement' is the wordplay.
'arrangement' indicates anagramming the letters.
'see'+'scales'='seescales'
'seescales' with letters rearranged gives 'CEASELESS'.
(Other definitions for ceaseless that I've seen before include "keeps on running" , "Going on continually, incessant" , "Interminable" , "Everlasting" , "Continuous" .)