One side of a leaf (4)
I believe the answer is:
page
This clue is a double definition.
'one side' is the first definition.
(I've seen this before)
'a leaf' is the second definition.
(I know that page is a type of leaf)
'of' acts as a link.
(Other definitions for page that I've seen before include "Leaf - young attendant" , "Attendant - this is on one!" , "Boy attendant; send out call for" , "Attendant - sheet" , "errand-boy" .)