Conscientious editing changed round novel's ending (8)
I believe the answer is:
diligent
'conscientious' is the definition.
(thesaurus)
'editing changed round novel's ending' is the wordplay.
'changed' is an anagram indicator.
'round' is an insertion indicator.
'ending' indicates one should take the final letters.
The last letter of 'novel' is 'l'.
'editing' with letters rearranged gives 'diigent'.
'diigent' enclosing 'l' is 'DILIGENT'.
(Other definitions for diligent that I've seen before include "Showing care and effort" , "Working hard and conscientiously" , "I tingled, being hard-working and conscientious" , "Putting care and effort into work" , "Steady in application and industry" .)