Bookcase part (5)
I believe the answer is:
shelf
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">bookcase part</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for shelf that I've seen before include "Ledge for books etc" , "Storage ledge" , "Ledge for holding things" , "Whereon 2 down is not!" , "Horizontal surface for holding things" .)