Difficult to support one sort of book (8)
I believe the answer is:
hardback
'one sort of book' is the definition.
(I've seen this before)
'difficult to support' is the wordplay.
'difficult' becomes 'hard' ('hard' can be a synonym of 'difficult').
'to support' becomes 'back' (back is a kind of support**).
'hard'+'back'='HARDBACK'
(Other definitions for hardback that I've seen before include "Book with stiff covers" , "Penguins are rarely so" , "Style of book binding" , "Book with board covers" , "Durable version of book" .)