Editor rejected stern feature (6)
I believe the answer is:
detail
'feature' is the definition.
(I've seen this in another clue)
'editor rejected stern' is the wordplay.
'editor' becomes 'ed' (abbreviation).
'rejected' says the letters should be written backwards.
'stern' becomes 'tail' (synonyms).
'ed' back-to-front is 'de'.
'de'+'tail'='DETAIL'
(Other definitions for detail that I've seen before include "A small or subordinate particular" , "Describe fully, give particulars of" , "soldiers given a special task" , "An individual item or element" , "Special military group" .)