Part of a plant and of a book (4)
I believe the answer is:
leaf
'part of a plant and of a book' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for leaf that I've seen before include "In fall, one dislocated" , "Thumb" , "Piece of reading material" , "Flick (through)" , "Thin sheet of metal" .)