Nine-sided shape (7)
I believe the answer is:
nonagon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nine-sided shape</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for nonagon that I've seen before include "Figure with nine sides" , "Nine sided figure" , "Nine-sided polygon" , "Figure with nine, twenty-one Dn" , "Nine-sided shape" .)