Flea jumped on piece of paper (4)
I believe the answer is:
leaf
'piece of paper' is the definition.
(leaf is a kind of piece of paper)
'flea jumped' is the wordplay.
'jumped' is an anagram indicator (I've seen 'jumping' mean this).
'flea' with letters rearranged gives 'LEAF'.
'on' acts as a link.
(Other definitions for leaf that I've seen before include "Part of tree or book" , "Page; piece of tree" , "Growth on plant" , "Turn over a new one to reform" , "Bit of tree, of book" .)