Unfinished heroic book is perfect example (7)
I believe the answer is:
epitome
'perfect example' is the definition.
(I've seen this before)
'unfinished heroic book' is the wordplay.
'unfinished' means to remove the last letter.
'heroic' becomes 'epic' ('epic' can be a synonym of 'heroic').
'book' becomes 'tome' (tome is a kind of book).
'epic' with its last letter removed is 'epi'.
'epi'+'tome'='EPITOME'
'is' acts as a link.
(Other definitions for epitome that I've seen before include "Summary of a written work" , "classic example" , "ie Tempo (anag.)" , "Typical example, prototype" , "Personification" .)