Writer's verse left unfinished (3)
I believe the answer is:
poe
'writer's' is the definition.
(Edgar Allan Poe)
'verse left unfinished' is the wordplay.
'verse' becomes 'poem' (I've seen this before).
'left unfinished' means to remove the last letter.
'poem' with its last letter taken off is 'POE'.
(Other definitions for poe that I've seen before include "Edgar Allan ..., American writer of the macabre" , "Edgar Allan --, US poet and author" , "The Raven writer" , "Edgar Allan . . ., American writer of horror stories" , "Name of writer" .)