New sort of book (5)
I believe the answer is:
novel
This clue is a double definition.
'new' is the first definition.
('novel' can be a synonym of 'new')
'sort of book' is the second definition.
(Other definitions for novel that I've seen before include "work of Dickens?" , "New sort of fiction?" , "book such as Brave New World" , "Volume of prose fiction" , "piece of writing" .)