Seven-sided shape (8)
I believe the answer is:
heptagon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">seven-sided shape</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 heptagon that I've seen before include "A geometric figure with seven sides" , "Seven-sided object" , "Seven-sided shape" , "Seven-sided figure" .)