The leader's opinion, aside from the letter writers (9)
I believe the answer is:
editorial
'the leader's' is the definition.
(type of newspaper article)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for editorial that I've seen before include "Statement of a newspaper's opinion" , "Article that states a newspaper's opinion" , "paper item" , "Article written" , "(Paper's) leader" .)