Finished unwritten poem (8)
I believe the answer is:
pastoral
'poem' is the definition.
(I've seen this before)
'finished unwritten' is the wordplay.
'finished' becomes 'past' (I've seen this in another clue).
'unwritten' becomes 'oral' (synonyms).
'past'+'oral'='PASTORAL'
(Other definitions for pastoral that I've seen before include "Bucolic, rural" , "of minister's duties" , "Letter to church members" , "Beethoven's 6th symphony ..." , "Of shepherds; pupil-welfare (responsibility)" .)