Finished chapter and left, thus upsetting editor (6)
I believe the answer is:
closed
'finished' is the definition.
(closing is a kind of finishing)
'chapter and left thus upsetting editor' is the wordplay.
'chapter' becomes 'c'.
'and' means one lot of letters go next to another.
'left thus' becomes 'sol' (I am not sure about this - if you are sure you should believe this answer much more).
'upsetting' is a reversal indicator.
'editor' becomes 'ed'.
'sol' backwards is 'los'.
'c'+'los'+'ed'='CLOSED'
Can you help me to learn more?
(Other definitions for closed that I've seen before include "Not longer open" , "successfully completed" , "Shut" , "Concluded or fastened" , "Terminated" .)