Fall faller (4)
I believe the answer is:
leaf
'fall faller' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for leaf that I've seen before include "Bit of foliage" , "Thumb" , "Piece of reading material" , "Hinged or removable table flap" , "Part of tree or book" .)