Article written in advance (6)
I believe the answer is:
leader
'article written in advance' is the definition.
'leader' can be an answer for 'article' (thesaurus). I'm not sure about the 'written in advance' bit.
'article written in advance' is the wordplay.
'article' becomes 'lead' (lead is a kind of article).
'written in advance' becomes 'er' (I can't explain this - if you can you should give a lot more credence to this answer).
'lead'+'er'='LEADER'
Can you help me to learn more?
(Other definitions for leader that I've seen before include "Main editorial in a newspaper" , "One inspires or guides others" , "Aliens demand to be taken to this man" , "Ruler" , "One is ahead and shows the way" .)