Show disapproval of unfinished volume (3)
I believe the answer is:
boo
'show disapproval of' is the definition.
(as in a crowd booing)
'unfinished volume' is the wordplay.
'unfinished' means to remove the last letter.
'volume' becomes 'book' (book is a kind of volume).
'book' with its final letter taken off is 'BOO'.
(Other definitions for boo that I've seen before include "Make one's dislike heard" , "Cry of contempt" , "Show displeasure orally" , "Poor reception" , "Disapproving sound" .)