Book containing revolutionary plant item (7)
I believe the answer is:
twosome
'item' is the definition.
(I've seen this before)
'book containing revolutionary plant' is the wordplay.
'book' becomes 'tome' (a tome is a book).
'containing' means one lot of letters goes inside another.
'revolutionary' says the letters should be written in reverse (letters revolve around).
'plant' becomes 'sow'.
'sow' back-to-front is 'wos'.
'tome' enclosing 'wos' is 'TWOSOME'.
(Other definitions for twosome that I've seen before include "Couple" , "Item" , "game of golf" , "match" , "Pair, duo" .)