Page of a book (4)
I believe the answer is:
leaf
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">page of a book</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for leaf that I've seen before include "Bit of foliage" , "Small part of wood" , "Page or piece of foliage" , "Flag" , "Bit of tree, of book" .)