Tough second book (8)
I believe the answer is:
hardback
'book' is the definition.
(hardback is a kind of book)
'tough second' is the wordplay.
'tough' becomes 'hard' (similar in meaning).
'second' becomes 'back' (to second a motion is to back it).
'hard'+'back'='HARDBACK'
(Other definitions for hardback that I've seen before include "Durable version of book" , "Book with stiff covers" , "Sort of book" , "Penguins are rarely so" , "It might be a novel!" .)